Move the USBPhy header files into usb/device/USBPhy. Also move hal
and target USB files since mbed 2 does not compile when these files
are present without the USBPhy headers.
Directory restructure summary:
platform/USBPhy*
to usb/device/USBPhy/USBPhy*
hal/*
to usb/device/hal/*
targets/TARGET_Freescale/usb/*
to usb/device/targets/TARGET_Freescale/*
targets/TARGET_NXP/TARGET_LPC176X/usb/*
to usb/device/targets/TARGET_NXP/*
Russ Butler