drm/i915/icl: Enable RC6 and RPS in Gen11

AFAICT, once the new interrupt is in place, the rest should behave the
same as Gen10.

v2: Update ring frequencies (Sagar)
v3: Rebase.

Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180405140052.10682-5-mika.kuoppala@linux.intel.com