A flag "link_power_control" is added to indicate whether a codec needs to
control the link power.  And a new bus ops link_power() is defined for the
codec to request to enable/disable the link power.
Signed-off-by: NMengdong Lin <mengdong.lin@intel.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>