drm: Unify radeon offset checking.

Replace r300_check_offset() with generic radeon_check_offset(), which doesn't
reject valid offsets when the framebuffer area is at the very end of the card's
32 bit address space. Make radeon_check_and_fixup_offset() use
radeon_check_offset() as well.

This fixes https://bugs.freedesktop.org/show_bug.cgi?id=7697 .
diff --git a/drivers/char/drm/radeon_state.c b/drivers/char/drm/radeon_state.c
index 6e04fdd..938eccb 100644
--- a/drivers/char/drm/radeon_state.c
+++ b/drivers/char/drm/radeon_state.c
@@ -43,10 +43,7 @@
 						    u32 *offset)
 {
 	u64 off = *offset;
-	u32 fb_start = dev_priv->fb_location;
-	u32 fb_end = fb_start + dev_priv->fb_size - 1;
-	u32 gart_start = dev_priv->gart_vm_start;
-	u32 gart_end = gart_start + dev_priv->gart_size - 1;
+	u32 fb_end = dev_priv->fb_location + dev_priv->fb_size - 1;
 	struct drm_radeon_driver_file_fields *radeon_priv;
 
 	/* Hrm ... the story of the offset ... So this function converts
@@ -66,8 +63,7 @@
 	/* First, the best case, the offset already lands in either the
 	 * framebuffer or the GART mapped space
 	 */
-	if ((off >= fb_start && off <= fb_end) ||
-	    (off >= gart_start && off <= gart_end))
+	if (radeon_check_offset(dev_priv, off))
 		return 0;
 
 	/* Ok, that didn't happen... now check if we have a zero based
@@ -81,11 +77,10 @@
 
 	/* Finally, assume we aimed at a GART offset if beyond the fb */
 	if (off > fb_end)
-		off = off - fb_end - 1 + gart_start;
+		off = off - fb_end - 1 + dev_priv->gart_vm_start;
 
 	/* Now recheck and fail if out of bounds */
-	if ((off >= fb_start && off <= fb_end) ||
-	    (off >= gart_start && off <= gart_end)) {
+	if (radeon_check_offset(dev_priv, off)) {
 		DRM_DEBUG("offset fixed up to 0x%x\n", (unsigned int)off);
 		*offset = off;
 		return 0;