This patch will allow the user to pass a function to calculate
the baud divisor.
This will allow for more flexibility, since for some BSPs
like raspberrypi, the calculation of baud divisor is different
from what is in the current driver.
The precision clock synthesizer support broke the driver on the QorIQ
P1020. On this device the Alternate Function Register is accessed with
DLAB == 1 instead of the FIFO Control Register (FCR). Restructure the
code to account for this.
Set the FIFO control register while DLAB == 1 in the line control
register. At least on the QorIQ T4240 the driver still works with the
re-ordered FIFO control register access.
