slimbus: Add Device Tree support for SLIMBUS

Slave devices can be added by listing them as child of a SLIMBUS
controller of_node in the Device Tree.
It is required to specify elemental address, and name of the slave
device.

Change-Id: Ie1b2f8fe58988f0237547a84f1bbb14ce4733eff
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>