drm/i915: Introduce CRTC output format

This patch adds an enum "intel_output_format" to represent
the output format of a particular CRTC. This enum will be
used to produce a RGB/YCBCR4:4:4/YCBCR4:2:0 output format
during the atomic modeset calculations.

V5:
- Created this separate patch to introduce and init output_format.
- Initialize parameters of output_format_str respectively (Jani N).
- Call it intel_output_format than crtc_output_format(Ville).
- Set output format in pipe_config for every encoder (Ville).
- Get rid of extra DRM_DEBUG_KMS during get_pipe_config (Ville)

V6: Rebase
V7: Fixed alignment warnings (checkpatch)
V8: Another check[atch warning for alignment
V9: Rebase
V10: Rebase on top of DSI restructure
V11: Addressed review comment from Ville
	- Set CRTC format for pre-HSW get_pipe_config() function too.
     Added Ville's R-B

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1539325394-20788-1-git-send-email-shashank.sharma@intel.com