drm/{i915, xe}/fbdev: deduplicate struct drm_mode_fb_cmd2 init

drm/{i915, xe}/fbdev: deduplicate struct drm_mode_fb_cmd2 init

[ Upstream commit f9ff39f940f5ddd1d4ffcff602de7206aa1ff05d ]

Pull struct drm_mode_fb_cmd2 initialization out of the driver dependent
code into shared display code.

v2: Rebase on xe stride alignment change

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/e922e47bfd39f9c5777f869ff23c23309ebbb380.1758184771.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Stable-dep-of: 460b31720369 ("drm/i915/fbdev: Hold runtime PM ref during fbdev BO creation")
Signed-off-by: Sasha Levin <sashal@kernel.org>