drm/sun4i: frontend: Move CSC bypass setup to format update routine

In order to support YUV to RGB conversion with the frontend (which is
generally used for connecting with the backend), the CSC block must not
be bypassed.

As a result, the bit to enable CSC bypass is moved from the runtime
resume routine to the format update routine, so that it can disabled
when introducing support for YUV formats later.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181123092515.2511-17-paul.kocialkowski@bootlin.com