drm/repaper: Use format helper for xrgb8888 to monochrome conversion

commit 1201597b858c7ace50009b28b8a01cf065d53fa8 from
https://nv-tegra.nvidia.com/r/3rdparty/canonical/linux-jammy.git jetson_36.3

There is now a drm_fb_xrgb8888_to_mono_reversed() helper function to do
format conversion from XRGB8888 to reversed monochrome.

Use that helper and remove the open coded version in the repaper driver.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220223193735.213185-1-javierm@redhat.com
(cherry picked from commit 24c6bede

)
Change-Id: If818b82863005b3f76cbefd2d6fe62036f38338d
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/3rdparty/canonical/linux-jammy/+/2985835
Reviewed-by: svcacv <svcacv@nvidia.com>
Reviewed-by: Jonathan Hunter <jonathanh@nvidia.com>
GVS: Gerrit_Virtual_Submit <buildbot_gerritrpt@nvidia.com>
Signed-off-by: Rajeshkumar Ramasamy <rajeshkumar.ramasamy@windriver.com>