drm/radeon: properly handle mc_stop/mc_resume on evergreen+ (v2)

- Stop the displays from accessing the FB
- Block CPU access
- Turn off MC client access

This should fix issues some users have seen, especially
with UEFI, when changing the MC FB location that result
in hangs or display corruption.

v2: fix crtc enabled check noticed by Luca Tettamanti

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/radeon/evergreend.h b/drivers/gpu/drm/radeon/evergreend.h
index 7934785..df542f1 100644
--- a/drivers/gpu/drm/radeon/evergreend.h
+++ b/drivers/gpu/drm/radeon/evergreend.h
@@ -87,6 +87,10 @@
 
 #define	CONFIG_MEMSIZE					0x5428
 
+#define	BIF_FB_EN						0x5490
+#define		FB_READ_EN					(1 << 0)
+#define		FB_WRITE_EN					(1 << 1)
+
 #define	CP_COHER_BASE					0x85F8
 #define	CP_STALLED_STAT1			0x8674
 #define	CP_STALLED_STAT2			0x8678
@@ -430,6 +434,9 @@
 #define		NOOFCHAN_MASK					0x00003000
 #define MC_SHARED_CHREMAP					0x2008
 
+#define MC_SHARED_BLACKOUT_CNTL           		0x20ac
+#define		BLACKOUT_MODE_MASK			0x00000007
+
 #define	MC_ARB_RAMCFG					0x2760
 #define		NOOFBANK_SHIFT					0
 #define		NOOFBANK_MASK					0x00000003