drm/tests: Add test for drm_framebuffer_init()

drm/tests: Add test for drm_framebuffer_init()

Add three KUnit test cases for the drm_framebuffer_init function:

1. Test if expected values are being set after drm_framebuffer_init() call.
2. Try to init a framebuffer without setting its format.
3. Try calling drm_framebuffer_init() with mismatch of the drm_device
   passed at the first argument and the one pointed by fb->dev.

Signed-off-by: Carlos Eduardo Gallo Filho <gcarlos@disroot.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240911001559.28284-9-gcarlos@disroot.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>