soc: qcom: Stub IPCRTR client driver

The IPCRTR channel needs to come up for the pronto block to be happy and
continue communication, so this driver does just that (and dumps
incoming data in the log).

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>

Conflicts:
	drivers/soc/qcom/Kconfig
	drivers/soc/qcom/Makefile