The test was constructed as a single function (test case) which checks
multiple conditions, calling the function that is tested multiple times
with different arguments.
This usually means that it can be easily converted into multiple test
cases.
Split igt_check_plane_state into two parameterized test cases,
drm_check_plane_state and drm_check_invalid_plane_state.

Passing output:
============================================================
============== drm_plane_helper (2 subtests) ===============
================== drm_check_plane_state ===================
[PASSED] clipping_simple
[PASSED] clipping_rotate_reflect
[PASSED] positioning_simple
[PASSED] upscaling
[PASSED] downscaling
[PASSED] rounding1
[PASSED] rounding2
[PASSED] rounding3
[PASSED] rounding4
============== [PASSED] drm_check_plane_state ==============
============== drm_check_invalid_plane_state ===============
[PASSED] positioning_invalid
[PASSED] upscaling_invalid
[PASSED] downscaling_invalid
========== [PASSED] drm_check_invalid_plane_state ==========
================ [PASSED] drm_plane_helper =================
============================================================
Testing complete. Ran 12 tests: passed: 12

v2: Add missing EXPECT/ASSERT (Maíra)
v3: Use single EXPECT insted of condition + KUNIT_FAILURE (Maíra)
v4: Rebase after "drm_test" rename
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Maíra Canal <mairacanal@riseup.net>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20221020082135.779872-2-michal.winiarski@intel.com