drm/vc4: Bring HDMI up from power off if necessary.

If the firmware hadn't brought up HDMI for us, we need to do its
power-on reset sequence (reset HD and and clear its STANDBY bits,
reset HDMI, and leave the PHY disabled).

Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/vc4/vc4_regs.h

@@ -456,6 +456,8 @@
 #define VC4_HDMI_TX_PHY_RESET_CTL		0x2c0
 
 #define VC4_HD_M_CTL				0x00c
+# define VC4_HD_M_REGISTER_FILE_STANDBY		(3 << 6)
+# define VC4_HD_M_RAM_STANDBY			(3 << 4)
 # define VC4_HD_M_SW_RST			BIT(2)
 # define VC4_HD_M_ENABLE			BIT(0)