ASoc: ABE VxREC: use VxREC audio back-end

VxREC is the back-end of MM_UL and MM_UL2.
VxREC back-end represents the Vx_REC input of the ROUTE_UL.
Vx_REC can be mono or stereo input even it mixes
different inputs such as Vx_UL, Vx_DL, TONES_DL and MM_DL.
This audio BE needs to start even none of its inputs
are enable. This is to avoid any cross-dependencies between
VxREC and Vx_UL, Vx_DL, TONES_DL and MM_DL that could make
userspace code much more complex.

Change-Id: Iebe8189951b9b77944f7ff8f180c7d977ecbef00
Signed-off-by: Francois Mazard <f-mazard@ti.com>
Signed-off-by: Pierre Moos <p-moos@ti.com>

Conflicts:
	sound/soc/omap/sdp4430.c
ASoC: OMAP ABE: Add support for single downlink path

ABE 09.56 allows connecting PDM_DL2 from DL1 path, which gives
the advantage of running hands-free path on lower OPP. DL2 path
can be enabled or disabled via config option: SND_OMAP_SOC_ABE_DL2.

Change-Id: I0c82d0507249630ff36627cfdb6523655da72734
Signed-off-by: Sebastien Guiriec <s-guiriec@ti.com>
Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
Tuna didn't like this, let's disable by default