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 <[e-mail]>
Cc: [e-mail]
Signed-off-by: Vineet Gupta <[e-mail]>

arch/arc/include/asm/fb.h

···
+#ifndef _ASM_FB_H_
+#define _ASM_FB_H_
+
+#include <linux/fb.h>
+#include <linux/fs.h>
+#include <asm/page.h>
+
+static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
+				unsigned long off)
+{
+	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+}
+
+static inline int fb_is_primary_device(struct fb_info *info)
+{
+	return 0;
+}
+
+#endif /* _ASM_FB_H_ */