drm/i915/vga: Include the current pipe in the VGA disable debug message

drm/i915/vga: Include the current pipe in the VGA disable debug message

Add some debugs to the VGA plane disable so that we can at least
see from the logs when it happens (and on which pipe). I was curious
about this at some point when I was seeing some random underruns
near the time when we disable the VGA plane, but I think in the end
that turned out to be a red herring.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250417114454.12836-5-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>