drm/i915: Lookup the memory region first in the BIOS FB takeover

When doing the BIOS FB takeover let's look up the appropriate
memory region first. If it doesn't exist there's not much point
in doing the PTE read/etc either.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250313140838.29742-9-ville.syrjala@linux.intel.com


Reviewed-by: Jouni Högander <jouni.hogander@intel.com>