usb: gadget: fsl-mxc-udc: replace cpu_is_xxx() with platform_device_id

As mach/hardware.h is deleted, we need to use platform_device_id to
differentiate SoCs. Besides, one cpu_is_mx35 is useless as it has
already used pdata to differentiate runtime

Meanwhile we update the platform code accordingly.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>