ALSA: hda - add AZX_DCAPS_I915_POWERWELL to Baytrail

This patch addes AZX_DCAPS_I915_POWERWELL to BYT (Baytrail).

Like Braswell and Skylake, the HDMI codec on Bytrail is also in the shared
power well with GPU. This power well must be turned on before we reset link
to probe the codec, to avoid communication failure with the codec.

The side effect is that this power is always ON in S0 because the BYT HDMI
codec does not support EPSS or D3ClkStop and so the controller doesn't enter
D3 at runtime, and the HDMI codec and analog codec share a single physical
HD-A link and so we cannot reset the HD-A link freely when we re-enable the
power to use the HDMI codec.

Next step is to test if an AGP reset or double AGP reset on BYT HDMI codec is
okay to bring the HDMI codec back to a functional state after restoring the
power. If okay, we can bind the power on/off with the HDMI codec PM without
interrupting the analog audio.

Signed-off-by: Mengdong Lin <mengdong.lin@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

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