usb: phy-msm-usb: Add reg-names device tree property

The current code is handling the iomem resources by index. It is working
fine today. Because there are only 1 required and 1 optional iomem
resources. The new targets have more optional iomem resources
and index based query may create problems. Use reg-names device tree
property to handle the iomem resources by name.

Change-Id: I1978edc9dbd8d176b01eb03b76450b77336f738b
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>