ASoC: msm: Add back-end enablement for CPU DAIs.

ALSA framework in kernel 3.4 requires all CPU DAIs to be routed to
the repective back-end input or output. Add the routing for STUB_1,
SLIMBUS_1, SLIMBUS_3, and SLIMBUS_4 CPU DAIs.

CRs-Fixed: 376720
Change-Id: Ie7799777d500194c53520320302e667f2ed07480
Signed-off-by: Neema Shetty <nshetty@codeaurora.org>