usb: otg: Fix USB remote-wakeup with LPM

Some of USB clocks have to be enabled in order for A2 to
be able to wake up USB.
Since USB now enters LPM upon USB bus suspend, this fix keeps
USB pclk & core_clk enabled, to allow waking up from A2.

A similar fix was already introduced for HSIC driver. This
change adds similar fix for USB.

Change-Id: Icd434132bc3dc3466dc7a55bb40603a3de3b4b2f
CRs-Fixed: 369189
Signed-off-by: Amit Blay <ablay@codeaurora.org>