The file is moved to hda core and renamed to hdac_i915.c, so can be used
by both legacy HDA driver and new Skylake audio driver.

- Add snd_hdac_ prefix to the public APIs.
- The i915 audio component is moved to core bus and dynamically allocated.
- A static pointer hdac_acomp is used to help bind/unbind callbacks to get
  this component, because the sound card's private_data is used by the azx
  chip pointer, which is a legacy structure. It could be removed if private
  _data changes to some core structure which can be extended to find the
  bus.
- snd_hdac_get_display_clk() is added to get the display core clock for
  HSW/BDW.
- haswell_set_bclk() is moved to hda_intel.c because it needs to write the
  controller registers EM4/EM5, and only legacy HD-A needs it for HSW/BDW.
- Move definition of HSW/BDW-specific registers EM4/EM5 to hda_register.h
  and rename them to HSW_EM4/HSW_EM5, because other HD-A controllers have
  different layout for the extended mode registers.
Signed-off-by: Mengdong Lin <mengdong.lin@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>