drm/tests: Add test cases for drm_rect_calc_hscale()

Insert parameterized test for the drm_rect_calc_hscale() to ensure
correctness and prevent future regressions. Besides the test for the
usual case, tests the exceptions.

Signed-off-by: Arthur Grillo <arthurgrillo@riseup.net>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230418230146.461129-3-arthurgrillo@riseup.net