arc: Add our own implementation of fb_pgprotect()

arc: Add our own implementation of fb_pgprotect()

During mmaping of frame-buffer pages to user-space
fb_protect() is called to set proper page settings.

In case of ARC we need to mark pages that are mmaped to
user as uncached because of 2 reasons:
 * Huge amount of data if passing through data cache will
   thrash cache a lot making cache almost useless for other
   less traffic hungry processes.
 * Data written by user in FB will be immediately available for
   hardware (such as PGU etc) without requirements to flush data
   cache regularly.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: linux-snps-arc@lists.infradead.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>