OMAP3: overo: add Alto35 expansion board support

Pin configuration per branched commit b96d959acd80:

  "Tweak pin mux for Alto35.  GPIOs 148 and 151 used.  Disable SPI CS1 as
  the screen configuration information is incorrect"

Modified to apply only to Alto35 boards and to initialize all LEDs and
user-controllable button.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>