firmware/sysfb: Set firmware-framebuffer parent device

Set the firmware framebuffer's parent device, which usually is the
graphics hardware's physical device. Integrates the framebuffer in
the Linux device hierarchy and lets Linux handle dependencies among
devices. For example, the graphics hardware won't be suspended while
the firmware device is still active.

v4:
	* fix build for CONFIG_SYSFB_SIMPLEFB=n, again
v3:
	* fix build for CONFIG_SYSFB_SIMPLEFB=n (Sui)
	* test result of screen_info_pci_dev() for errors (Sui)
v2:
	* detect parent device in sysfb_parent_dev()

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240212090736.11464-4-tzimmermann@suse.de