tests/i915: Exercise coherency of mmapped frame buffers

Visible glitches have been observed when running graphics applications on
Linux under Xen hypervisor.  Those observations have been confirmed with
failures from kms_pwrite_crc IGT test that verifies data coherency of DRM
frame buffer objects using hardware CRC checksums calculated by display
controllers, exposed to userspace via debugfs.  Since not all applications
exhibit the issue, we need to exercise more methods than just pwrite in
order to identify all affected processing paths.

Create a new test focused on exercising coherency of future scanout
buffers populated over mmap.  Cover all available mmap methods and caching
modes expected to be device coherent.

v3: Drop redundant prerequisite checks (Andrzej),
  - if (condition) return; construct gives shorter code than
    if (!condition) continue; (Andrzej),
  - gem_has_lmem() implies gem_has_mmap_offset(), flatten related nested
    conditions.
v2: Drop unused functions -- left-overs from unsuccessful negative subtest
    attempts requiring consistent crc mismatches in non-coherent modes,
  - since all subtests now call igt_assert_crc_equal(), move it from
    subtest bodies to an updated and renamed helper,
  - drop "derived from ..." info from copyrights comment (Kamil),
  - fix order of includes (Kamil),
  - fix whitespace (Kamil),
  - Cc: Bhanuprakash (Kamil).

Link: https://gitlab.freedesktop.org/drm/intel/-/issues/7648


Cc: Bhanuprakash Modem <bhanuprakash.modem@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>