ASoC: msm: Implementing Tx mute in ASM loopback

Adding TX Mute functionality in ASM Loopback.
ASM loopback in the TX session uses Multimedia6,
applying mute/ummute asm commands on Multimedia6.

CRs-Fixed: 995988
Change-Id: I4caa5964f4fc774e33d9666f89b896f15e160943
Signed-off-by: Surendar karka <sukark@codeaurora.org>