drm/i915/dsc: rename crtc state dsc_params member to dsc

Reduce verbosity in code by renaming dsc_params member of crtc state to
simply dsc. There is enough context for this to be clear. No functional
changes.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022133414.8293-1-jani.nikula@intel.com