drm/i915/cnp: Wa 1181: Fix Backlight issue

drm/i915/cnp: Wa 1181: Fix Backlight issue

This workaround fixes a CNL PCH bug when changing
backlight from a lower frequency to a higher frequency.

During random reboot cycles, display backlight seems to
be off/ dim for 2-3 mins.

The only functional change on this patch is to
set bit 13 of 0xC2020 for CNL PCH.

The rest of patch is organizing identation around
those bits definitions and re-organizing CFL workarounds.

v2: Only add the bit that matters without touching others
    around (Jani).
    Rebase on top of clock gating functions rename.

Cc: Jani Nikula <[email protected]>
Cc: Arthur J Runyan <[email protected]>
Cc: Dhinakaran Pandiyan <[email protected]>
Signed-off-by: Rodrigo Vivi <[email protected]>
Reviewed-by: Dhinakaran Pandiyan <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]