msm: bam_dmux: enable disconnect ack feature support by default

The disconnect ack feature is normally turned on by a handshaking
mechanism between bam_dmux and A2, but on some 9615 variants that
mechanism will not exist.  A2 will still expect the disconnect ack to
be active and might crash if it encounters that it is not active.
Enable the disconnect ack feature by default to prevent this.

CRs-Fixed: 372958
Change-Id: I2222b4651e14c2154f51a8c38852a855cdd93c4e
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>