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

Replace the architecture's fbdev helpers with the generic ones
from <asm-generic/fb.h>. On PARISC, 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: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230417125651.25126-15-tzimmermann@suse.de