drm/i915: Power well id for ICL PG3

Gen11 onwards PG3 is contains functions for pipe B,
external displays, and VGA. It make sense to add
a power well id with name ICL_DISP_PW_3 rather then
TGL_DISP_PW_3, Also PG3 power well id requires to
know if lpsp is enabled.

Reviewed-by: Animesh Manna <animesh.manna@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200415170555.15531-2-anshuman.gupta@intel.com