ASoC: msm: Add support for external EC reference point
ASoC: audio: Fix BE not disconnected even codec teardown

Scenario:
When FE1(LowLatency) comes in which opens BE1 and puts it in state
SND_SOC_DPCM_STATE_START. Similarly FE2(LPA) comes in with
connecting to same BE. Now FE2 is in SND_SOC_DPCM_STATE_PREPARE
state and waits for TRIGGER_START. Meanwhile FE1 is closed which
doesn't affect BE1 and FE2 which are connected.
Also, for FE2 pcm_close is called before TRIGGER_START itself.
In such a case, BE1 is not getting disconnected (afe_close is
not called) while Codec is teared down resulting in Slimbus
overflow.

Fix:
Whenever BE1 is found to be in SND_SOC_DPCM_STATE_START state
and FE1 being connected is not started yet, and close sequence
happens for this FE, then allow hw_free to happen for BE1 if
this is the only FE connected to this BE1. This allows BE to be
disconnected which calls afe_close then followed by Codec teardown
not resulting in any Slimbus overflows.

CRs-Fixed: 468118
Change-Id: I03a80a12c1fd0cf09bd2e3dfe1f1eb56589016d3
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>