drm/i915/tgl: Enabling DSC on Pipe A for TGL

DSC was not supported on Pipe A for previous platforms. Tigerlake onwards,
all the pipes support DSC. Hence, the DSC and FEC restriction on
Pipe A needs to be removed.

v2: Changes in the logic around removing the restriction around
    Pipe A (Manasi, Lucas)

Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Madhumitha Tolakanahalli Pradeep <madhumitha.tolakanahalli.pradeep@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190823004655.28905-1-madhumitha.tolakanahalli.pradeep@intel.com