drm/vc4: Add support for double-clocked modes.

Now that we have infoframes to report the pixel repeat flag, we can
start using it.  Fixes locking the 720x480i and 720x576i modes on my
Dell 2408WFP.  Like the 1920x1080i case, they don't fit properly on
the screen, though.

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

drivers/gpu/drm/vc4/vc4_regs.h

@@ -175,6 +175,8 @@
 # define PV_CONTROL_CLR_AT_START		BIT(14)
 # define PV_CONTROL_TRIGGER_UNDERFLOW		BIT(13)
 # define PV_CONTROL_WAIT_HSTART			BIT(12)
+# define PV_CONTROL_PIXEL_REP_MASK		VC4_MASK(5, 4)
+# define PV_CONTROL_PIXEL_REP_SHIFT		4
 # define PV_CONTROL_CLK_SELECT_DSI_VEC		0
 # define PV_CONTROL_CLK_SELECT_DPI_SMI_HDMI	1
 # define PV_CONTROL_CLK_SELECT_MASK		VC4_MASK(3, 2)