drm/exynos: fimd: Make plane alpha configurable

The fimd hardware supports variable plane alpha. Currently planes
are opaque, make this configurable.

Tested on TRATS2 with Exynos 4412 CPU, on top of linux-next-20181019.

Signed-off-by: Christoph Manszewski <c.manszewski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

include/video/samsung_fimd.h

@@ -211,6 +211,7 @@
 #define WINCON0_BPPMODE_24BPP_888		(0xb << 2)
 
 #define WINCON1_LOCALSEL_CAMIF			(1 << 23)
+#define WINCON1_ALPHA_MUL			(1 << 7)
 #define WINCON1_BLD_PIX				(1 << 6)
 #define WINCON1_BPPMODE_MASK			(0xf << 2)
 #define WINCON1_BPPMODE_SHIFT			2