drm/format-helper: Export drm_fb_clip_offset()

commit a79b92d323b5c3536433ca03d2ae093ea8c5524e from
https://nv-tegra.nvidia.com/r/3rdparty/canonical/linux-jammy.git jetson_36.3

Provide a function that computes the offset into a blit destination
buffer. This will allow to move destination-buffer clipping into the
format-helper callers.

v4:
	* add missing '@' for parameter documentation
	* fix typo 'frambuffer'
v2:
	* provide documentation (Sam)
	* return 'unsigned int' (Sam, Noralf)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211110103702.374-2-tzimmermann@suse.de
(cherry picked from commit 452290f3

)
Change-Id: I6da403e4d330fcc6a1948d3fa5f9b70f717c6758
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/3rdparty/canonical/linux-jammy/+/2985823
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>