fbdev/simplefb: Request memory region in driver

Requesting the framebuffer memory in simpledrm marks the memory
range as busy. This used to be done by the firmware sysfb code,
but the driver is the correct place.

v2:
	* store memory region in struct for later cleanup (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220125091222.21457-5-tzimmermann@suse.de