imx: serial: add IrDA support to serial driver

Using the iMX serial driver with an IrDA device
needs extra peripheral settings and specific
timing depending on the transmitter circuitry used.

Signed-off-by: Fabian Godehardt <fg@emlix.com>
Signed-off-by: Oskar Schirmer <os@emlix.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>