arch/loongarch: Implement <asm/fb.h> with generic helpers

mainline inclusion
from mainline-v6.5-rc1
commit 84998fc1
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7MWTU


CVE: NA

--------------------------------

Replace the architecture's fbdev helpers with the generic
ones from <asm-generic/fb.h>. No functional changes.

v2:
	* use default implementation for fb_pgprotect() (Arnd)

Signed-off-by: Yongzhen Zhang <zhangyongzhen@kylinos.cn>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230417125651.25126-7-tzimmermann@suse.de