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

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: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Acked-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230417125651.25126-17-tzimmermann@suse.de