defconfig: msm9615: enable usb bus suspend

Add USB_BUS_SUSPEND feature which needs to be defined once
CONFIG_PM_RUNTIME is defined in order for USB host mode to function.

CRs-Fixed: 385860
Change-Id: I68ab6692c086668205ef33507c6d98c3e8db484b
Signed-off-by: Shimrit Malichi <smalichi@codeaurora.org>