USB: Add driver for NXP ISP1301 USB transceiver

This new driver registers the NXP ISP1301 chip via the I2C subsystem.  The chip
is the USB transceiver shared by ohci-nxp, lpc32xx_udc (gadget) and
isp1301_omap.

ISP1301 is a very low-level driver that primarily separates out the I2C client
registration of the ISP1301 chip (including instantiation via DT), used by
other drivers, and declares the chip's registers. It's only a helper driver for
some OHCI and USB device drivers.  The driver can be considered as a register
set extension of ohci-nxp, lpc32xx-udc and isp1301_omap, which in turn know
best what to do with the low level functionality (individual ISP1301 registers
and timing, see the different initialization strategies in those drivers).
Those drivers previously internally duplicated ISP1301 register definitions
which is solved by this new isp1301 driver. The ISP1301 registers exposed via
isp1301.h can be accessed by other drivers using it with standard i2c_smbus_*()
accesses.

Following patches let the respective USB host and gadget drivers use this
driver, instead of duplicating ISP1301 handling.

Signed-off-by: Roland Stigge <stigge@antcom.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>