fbdev/efifb: Replace references to global screen_info by local pointer

Get the global screen_info's address once and access the data via
this pointer. Limits the use of global state.

v3:
	* use const screen_info in several places (Sui)
	* fix build for deferred takeover (kernel test robot)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231206135153.2599-2-tzimmermann@suse.de