msm: bam_dmux: add A2 power collapse support

The A2 hardware consumes a significant ammount of power when idle.  Add
support to disconnect and reconnect to the A2 when it powers up and down.
Also add support to vote against power collapse when the A2 is needed for
uplink data transmission.

Change-Id: I37c56c91ef2e0f6ba1e16a3c8cf6e5fe10817896
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>