drm/vc4: Use .pixel_order instead of custom .flip_cbcr

The hardware has enums for altering the Cr and Cb order,
so use this instead of having a flag which swaps the
order the pointers are presented to the hardware
(that only worked for 3 plane formats anyway).

Explicitly sets .pixel_order in each case, rather than
relying on then default XYCBCR order being a value 0.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/563872b69c1e5df142cb15ebfca7f20056b8a64c.1510841336.git.dave.stevenson@raspberrypi.org