ARM: dts: am3517-evm: Add support for UI board and Audio

The full AM3517-EVM shipped with an add-on board which contained
two Audio codecs, a GPIO expander with a variety of buttons, and
some other features.  This patch enables these portions of the UI
board because they don't directly conflict with existing features.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>