ext: Add the NoMali GPU no-simulation library

Add revision 9adf9d6e2d889a483a92136c96eb8a434d360561 of NoMali-model
from https://github.com/ARM-software/nomali-model. This library
implements the register interface of the Mali T6xx/T7xx series GPUs,
but doesn't do any rendering. It can be used to hide the effects of
software rendering.