Add tests/gem_exec_parse_blt

For testing blitter engine command parser on gen9.

v2: bad jump offset
v3: rebase
v4: improve bb start and subcase it
v5: fix presumed offsets (Jon)
v6: name, remove spurious gem_syncs (Chris)
v7: jump further backwards (Daniel), ctx_param_engines (Chris)
v8: dont mess up the Makefiles

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>