drm/vc4: dsi: Convert to use atomic operations

The atomic calls are preferred as the non-atomic ones
are deprecated. In preparation for conversion to a bridge,
switch to the atomic calls.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20221207-rpi-dsi-bridge-v1-4-8f68ee0b0adb@cerno.tech


Signed-off-by: Maxime Ripard <maxime@cerno.tech>