OMAP: SERIAL: Enable omap-serial driver in Kconfig

Enable omap-serial driver in /mach-omap2/Kconfig and
move 8250 driver selection for zoom boards. With omap-serial
driver addition all omap-uarts can be handled with
omap-serial driver.

With addition of omap-serial driver console parameter
needs be changed in bootargs from ttyS* should be
replaced with ttyO* [O --> OMAP not ZERO]

For example: ttyS0[UART1 on 3430SDP] changes to ttyO0.

But with some boards that do not use omap-uart as console uart.
we need to handle them with 8250 driver. Ex: ZOOM2/3.
For zoom2/3 board we need to use 8250 serial driver and
console parameter will remain ttyS0 which basically uses
a Quad uart placed on the debug board connected through a
gpio line.

Signed-off-by: Govindraj.R <govindraj.raja@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>