drm/i915/audio: s/ilk/ibx/

Rename the ilk stuff to ibx, as the audio logic lives
in the PCH. The only exception are VLV/CHV but their audio
hardware was stolen from ibx so the name still fits.

Also most of the register defines also use the IBX namespace.

Cc: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Cc: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230124144628.4649-13-ville.syrjala@linux.intel.com