The DaVinci SoCs have 3 uarts so enable all three by setting
CONFIG_SERIAL_8250_NR_UARTS and CONFIG_SERIAL_8250_RUNTIME_UARTS
to 3.

The other changes to the defconfig file are artifacts of running
the old defconfig through 'make config'.
Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>