hal: Do not force mono for VoIP Rx with stock configuration

HAL forces mono configuration for VoIP. This is due to VoIP
topology being configured as mono. However, pure AOSP
targets support VoIP with stereo configuration. HAL forcing
mono would lead to mismatched configuration. Correct this by
forcing mono only on vendor enhanced targets.

Change-Id: Icc63e14469ef67b5d916cebdba56a45910dcf28d