serial: add OMAP-specific defines

OMAP has some extra Interrupt types which can
be really useful for SW. Let's define them
so we can later use those in OMAP's serial driver.

Tested-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>