drm/i915: Allow platforms to share power well descriptors

Some power wells - like always-on and skl+/icl+ PW_1 - with the same
name, domain list, flags, ops are used by multiple platforms, so allow
platforms to reuse the descriptors of such power wells.

This change also lets the follow up patches to simplify the DG1/RKL
power well definitions, and remove the ADL-S skip_mask special casing.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220414210657.1785773-11-imre.deak@intel.com