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.

SConstruct

@@ -1202,6 +1202,10 @@ main.SConscript('ext/dramsim2/SConscript',
 main.SConscript('ext/drampower/SConscript',
                 variant_dir = joinpath(build_root, 'drampower'))
 
+# nomali build is shared across all configs in the build root.
+main.SConscript('ext/nomali/SConscript',
+                variant_dir = joinpath(build_root, 'nomali'))
+
 ###################################################
 #
 # This function is used to set up a directory with switching headers