drm/dp/dsc: Add Support for all BPCs supported by TGL

DSC engine on ICL supports only 8 and 10 BPC as the input
BPC. But DSC engine in TGL supports 8, 10 and 12 BPC.
Add 12 BPC support for DSC while calculating compression
configuration.

v2: Remove the separate define TGL_DP_DSC_MAX_SUPPORTED_BPC
and use the value directly.(More such defines can be removed
as part of future patches). (Ville)

v3: Use values directly instead of accessing the defines
everytime for min and max DSC BPC.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190820223059.18052-1-anusha.srivatsa@intel.com