drm/amdgpu: Pass along the format info from .fb_create() to drm_helper_mode_fill_fb_struct()

Plumb the format info from .fb_create() all the way to
drm_helper_mode_fill_fb_struct() to avoid the redundant
lookup.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250701090722.13645-10-ville.syrjala@linux.intel.com