drm/vc4: crtc: Support odd horizontal timings on BCM2712

BCM2711 runs pixelvalve at two pixels per clock cycle which results
in an unfortunate limitation that odd horizontal timings are not
possible. This is apparent on the standard DMT mode of 1366x768@60
which cannot be driven with correct timing.

BCM2712 defaults to the same behaviour, but has a mode to support
odd timings. While internally it still runs at two pixels per clock,
setting the PV_VCONTROL_ODD_TIMING bit makes it appear externally
to behave as it is one pixel per clock.

Switching to this mode fixes 1366x768@60 mode, and other custom
resultions with odd horizontal timings.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>