i915 specific test is added to validate max source size. This
test is expected to return -EINVAL for platforms where we have
max source width 4096 whereas it will pass on platforms having
max source width 5120. We have created fb of size 5120x4320
(=size of source) and downscaled to 3840x2160(=size of dest).

On MTL(disp_ver=14), in dmesg we can see

[drm:skl_update_scaler [i915]] scaler_user index 0.0: src
5120x4320 dst 3840x2160 size is out of scaler range.

since max source width supported is 4096 whereas same test
will pass on ADLP(display_ver=13) since max source width
supported is 5120.

v2: -updated comment (JP)
    -not declare list of tests (JP)
    -fixed indentation (JP)
    -added i915_max_source_size_test() inside
     igt_subtest_group() (JP)
v3: -added restriction to run this test only when HDISPLAY=3840
v4: -remove inner loop (JP)
    -test for HDISPLAY >= 3840 (JP)
v5: -override mode with lowest vrefresh to avoid cdclk lim (JP)
v6: -add VDISPLAY check (JP)
    -add description for find_mode() (JP)
v7: -pipe does not need to be set twice for output in same commit
     (JP)

Signed-off-by: Swati Sharma <swati2.sharma@intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>