slimbus: Allow controller to specify logical addresses

It is possible that the controller has fixed addressing table for
enumeration devices. In that case, logical address will be set by
controller and not by framework. get_laddr allows a controller to
assign logical address. Make sure framework allows such addressing
by not assuming that index into address table will represent logical
address.

Change-Id: I0e3873980c2ee2ece01237f450ecefff4e99aedc
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>