drm/i915/color: move CHV CGM pipe mode read to intel_color

Add color .get_config hook to read config other than LUTs and CSCs, and
start off with CHV CGM pipe mode to abstract the platform specific
register access better.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1444200931ae61b6360e3dcad8cbea206ad62e2f.1692287501.git.jani.nikula@intel.com