ARM: OMAP2+: UART: Add default mux for all uarts.

Padconf wakeup is used to wakeup uart after uart fclks/iclks are gated.
Rx-Pad wakeup was done by writing to rx-pad offset value populated in
serial.c idle_init. Remove the direct reading and writing into rx pad.
Remove the padconf field part of omap_uart_state struct and pad offsets
populated.

Now with mux framework support we can use mux_utilities
along with hmwod framework to handle io-pad configuration and enable rx-pad
wake-up mechanism.

To avoid breaking any board support add default mux data for all uart's
if mux info is not passed from board file.
With the default pads populated in serial.c wakeup capability for
rx pads is set, this can be used to enable uart_rx io-pad wakeup from
hwmod framework. The pad values in 3430sdp/4430sdp/omap4panda board file
are same as the default pad values populated in serial.c. Remove pad values
from 3430sdp/4430sdp/omap4panda board file and use the default pads
from serial.c file.

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