drm/radeon: update line buffer allocation for dce6

commit 290d24576ccf1aa0373d2185cedfe262d0d4952a upstream.

We need to allocate line buffer to each display when
setting up the watermarks.  Failure to do so can lead
to a blank screen.  This fixes blank screen problems
on dce6 asics.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=64850

Based on an initial fix from:
Jay Cornwall <jay.cornwall@amd.com>

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/radeon/sid.h b/drivers/gpu/drm/radeon/sid.h
index 45e240d..1767ae7 100644
--- a/drivers/gpu/drm/radeon/sid.h
+++ b/drivers/gpu/drm/radeon/sid.h
@@ -57,6 +57,10 @@
 
 #define DMIF_ADDR_CALC  				0xC00
 
+#define	PIPE0_DMIF_BUFFER_CONTROL			  0x0ca0
+#       define DMIF_BUFFERS_ALLOCATED(x)                  ((x) << 0)
+#       define DMIF_BUFFERS_ALLOCATED_COMPLETED           (1 << 4)
+
 #define	SRBM_STATUS				        0xE50
 
 #define	CC_SYS_RB_BACKEND_DISABLE			0xe80