ALSA: hda - Simplify CONFIG_SND_HDA_I915 condition

CONFIG_SND_HDA_I915 doesn't have to be user-selectable as this is almost
mandatory when i915 driver is available.  Let's enable it always when
CONFIG_DRM_I915 is set, so that user won't be bothered by useless
questions.

Signed-off-by: Takashi Iwai <tiwai@suse.de>