smd: perform SMD channel scanning synchronously at probe

When using the board-file probe order optimizations, the following
sequence is executed early on kernel boot:

	- msm_smd_init()
	- msm_rpm_smd_init()

When msm_smd_init() is invoked, it sets up it's data structures and then
invokes smd_post_init(), which places the probe work item in the
workqueue.

However, it's possible that msm_rpm_smd_init() is executed before SMD's
probe work is even invoked.  In this case, the rpm-smd driver requests
access to the 'rpm_requests' channel, but because the SMD channels have
yet to be scanned, it does not exist.

Workaround this issue by forcing channel scanning to happen immediately
in msm_smd_post_init().

Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>