base: Introducing utility for writing raw data in png format

Originally it was possible to use a Bitmap writer class for dumping a
framebuffer snapshot in a .bmp file. This patch enables you to choose
another format. In particular it implements the writing of PNG Images
using libpng library. The latter has to be already installed in your
machine, otherwise gem5 will default to the Bitmap format. This
configurable writer has been introduced in the VNC frame dumping mechanism,
which is storing changed frame buffers from the VNC server

Change-Id: Id7e5763c82235f1ce90381c8486b85a7cce734ce
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5181
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

base: Make the VNC server more resilient.

If the client does something bad, don't kill the whole simulation, just
complain, drop the client and keep going.

Change-Id: I824f2d121e2fe03cdf4323a25c192b68e0370acc
Reviewed-on: https://gem5-review.googlesource.com/3200
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

misc: Remove redundant compiler-specific defines

This patch moves away from using M5_ATTR_OVERRIDE and the m5::hashmap
(and similar) abstractions, as these are no longer needed with gcc 4.7
and clang 3.1 as minimum compiler versions.

base: Redesign internal frame buffer handling

Currently, frame buffer handling in gem5 is quite ad hoc. In practice,
we pass around naked pointers to raw pixel data and expect consumers
to convert frame buffers using the (broken) VideoConverter.

This changeset completely redesigns the way we handle frame buffers
internally. In summary, it fixes several color conversion bugs, adds
support for more color formats (e.g., big endian), and makes the code
base easier to follow.

In the new world, gem5 always represents pixel data using the Pixel
struct when pixels need to be passed between different classes (e.g.,
a display controller and the VNC server). Producers of entire frames
(e.g., display controllers) should use the FrameBuffer class to
represent a frame.

Frame producers are expected to create one instance of the FrameBuffer
class in their constructors and register it with its consumers
once. Consumers are expected to check the dimensions of the frame
buffer when they consume it.

Conversion between the external representation and the internal
representation is supported for all common "true color" RGB formats of
up to 32-bit color depth. The external pixel representation is
expected to be between 1 and 4 bytes in either big endian or little
endian. Color channels are assumed to be contiguous ranges of bits
within each pixel word. The external pixel value is scaled to an 8-bit
internal representation using a floating multiplication to map it to
the entire 8-bit range.

arch: Header clean up for NOISA resurrection

This patch is a first step to getting NOISA working again. A number of
redundant includes make life more difficult than it has to be and this
patch simply removes them. There are also some redundant forward
declarations removed.

base: split out the VncServer into a VncInput and Server classes

This patch adds a VncInput base class which VncServer inherits from.
Another class can implement the same interface and be used instead
of the VncServer, for example a class that replays Vnc traffic.

VNC: Add support for capturing frame buffer to file each time it is changed.

When a change in the frame buffer from the VNC server is detected, the new
frame is stored out to the m5out/frames_*/ directory. Specifiy the flag
"--frame-capture" when running configs/example/fs.py to enable this behavior.

includes: sort all includes

VNC: Add VNC server to M5