tests: Add kms_mmap_write_crc for cache coherency tests

This program can be used to detect when the writes don't land in scanout due
cache incoherency. Although this seems a problem inherently of non-LCC machines
("Atom"), this particular test catches a cache dirt on scanout on LLC machines
as well. It's inspired in Ville's kms_pwrite_crc.c and can be used also to test
the correctness of the driver's begin_cpu_access (TODO end_cpu_access).

To see the need for flush, one has to run this same binary a few times cause
it's not 100% reproducible (in my Core machine it's always possible to catch
the problem by running it at most 5 times).

Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>

tests/.gitignore

@@ -140,6 +140,7 @@ kms_force_connector
 kms_frontbuffer_tracking
 kms_legacy_colorkey
 kms_mmio_vs_cs_flip
+kms_mmap_write_crc
 kms_pipe_b_c_ivb
 kms_pipe_crc_basic
 kms_plane