USB: serial: FTDI: add high speed device support

Added support for FTDI's USB 2.0 hi-speed devices - FT2232H (2
interfaces) and FT4232H (4 interfaces), including a new baud rate
calculation for these devices which can now achieve up to 12Mbaud by
turning off a divide by 2.5 in the baud rate generator of the chips.  In
order to achieve baud rates of <1200 baud, the divide by 2.5 must be
active.  The default product ID of the FT2232H is 0x6010 (same as the
FT2232C IC).  The default PID of the FT4232H is 0x6011.


Signed-off-by: Mark J. Adamson <mark.adamson@ftdichip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>