drm/xe/display: Move remapped plane loop out of __xe_pin_fb_vma_dpt

drm/xe/display: Move remapped plane loop out of __xe_pin_fb_vma_dpt

In preparation for adding support for the auxccs plane lets move the
plane iteration loop to its own function.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Cc: Michael J. Ruhl <michael.j.ruhl@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patch.msgid.link/20260324084018.20353-9-tvrtko.ursulin@igalia.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>