drm/radeon/cik: add hw cursor support (v2)

CIK (DCE8) hw cursors are programmed the same as evergreen
(DCE4) with the following caveats:
- cursors are now 128x128 pixels
- new alpha blend enable bit

v2: rebase

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_mode.h

@@ -307,6 +307,8 @@ struct radeon_crtc {
 	uint64_t cursor_addr;
 	int cursor_width;
 	int cursor_height;
+	int max_cursor_width;
+	int max_cursor_height;
 	uint32_t legacy_display_base_addr;
 	uint32_t legacy_cursor_offset;
 	enum radeon_rmx_type rmx_type;