sparc: Pull more StaticInst base classes out of the ISA desc.

These are for the trap and branch instructions.

Change-Id: Idedab6f3e6c6c954c1f8a36dae52976cf25ad394
Reviewed-on: https://gem5-review.googlesource.com/5461
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>