USB: serial: f81232: add F81534A support

The Fintek F81532A/534A/535/536 is USB-to-2/4/8/12 serial ports device
and the serial port is default disabled when plugin computer.

The IC is contains devices as following:
	1. HUB (all devices is connected with this hub)
	2. GPIO/Control device. (enable serial port and control GPIOs)
	3. serial port 1 to x (2/4/8/12)

It's most same with F81232, the UART device is difference as follow:
	1. TX/RX bulk size is 128/512bytes
	2. RX bulk layout change:
		F81232: [LSR(1Byte)+DATA(1Byte)][LSR(1Byte)+DATA(1Byte)]...
		F81534A:[LEN][Data.....][LSR]

Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
[johan: reword an error message]
Signed-off-by: Johan Hovold <johan@kernel.org>