usb: phy: qmp: Configure AHB2PHY for one wait state read/writes

Prior to initializing the QMP PHY, it is recommended to configure
the AHB2PHY bridge to operate with one wait state reads and writes.
Add support for this by adding an optional register to the device
tree binding that points to the PERIPH_SS_AHB2PHY register space.

While at it, also convert the existing devm_ioremap_nocache()
call to use devm_ioremap_resource() which also validates and
performs a request_mem_region() on the IO resource.

Change-Id: Ibeaed03b24046b9c6deadcc2d83d329bece7ec26
Signed-off-by: Jack Pham <jackp@codeaurora.org>