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

Replace the architecture's fbdev helpers with the generic ones from
<asm-generic/fb.h>. On arc, pgprot_writecombine() and pgprot_noncached()
are the same; hence no functional changes.

v3:
	* use default implementation for fb_pgprotect() (Arnd)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Vineet Gupta <vgupta@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230417125651.25126-3-tzimmermann@suse.de