ASoC: apq8084: Add run-time PM support for voice over Bluetooth.

When external modem is paired with the apps processor, voice call
over BT uses Slimbus to transfer voice packets from the modem to
the application processor. Enable run-time PM so that Slimbus
driver keeps the clocks enabled in the BT usecase.

Change-Id: Ice9b50877049fe1edfc028035cf3005e50bd722d
Signed-off-by: Vidyakumar Athota <vathota@codeaurora.org>