ARM: OMAP2+: UART: Fix incorrect population of default uart pads

Commit (7496ba30  ARM: OMAP2+: UART: Add default mux for all uarts)
wrongly added muxing of default pads for all uarts. This causes
breakage on multiple boards using uart pins for alternate functions.

For example, on zoom3 random oopses can be seen with nfsroot as
the smsc911x ethernet FIFO timings on GPMC bus are controlled
by gpmc_wait2 and gpmc_wait3 pins. This means we can't mux these
pads to uart4 functionality as commit 7496ba30 was doing.

Not all boards tend to use all uarts and most of unused uart pins
are muxed for other purpose. This commit breaks the modules which
where trying to use unused uart pins on their boards.

So remove the default pad muxing. Note that this is not a complete
fix, as we now rely on bootloader set muxing for the uart wake-up
events. Further patching is needed to enable wake-up events for
uarts that are already muxed to uart mode.

Cc: Felipe Balbi <balbi@ti.com>
Cc: Kevin Hilman <khilman@ti.com>
Acked-by: Russ Dill <russ.dill@gmail.com>
Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Govindraj.R <govindraj.raja@ti.com>
[tony@atomide.com: updated comments to describe oops on zoom3]
Signed-off-by: Tony Lindgren <tony@atomide.com>