drm/i915/dmc: Reload pipe DMC state on TGL when enabling pipe A

drm/i915/dmc: Reload pipe DMC state on TGL when enabling pipe A

On TGL/derivatives the entire pipe DMC state (program + MMIO) is
lost when PG1 is disabled, and the main DMC does not restore
any of it. Reload the state when enabling a pipe.

The other option would be to not load the pipe DMC at all since
it's only needed for "fast LACE" (which we don't use) on these
platforms. But let's keep it around just in case we ever decide
that "fast LACE" is something we want.

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250617170759.19552-6-ville.syrjala@linux.intel.com