davinci: DA830/OMAP-L137 EVM: use runtime detection for UI card

This patch supports runtime detection of DA830 UI card and
eliminates the need for DA830_UI config option. Successful
probe of GPIO expander present on the UI card is used to
detect its presence. For this reason, GPIO_PCF857X is auto-
selected when DA830 EVM is configured. In case the UI card
is absent, the probe fails in reasonable time.

As a side effect this patch also gets rid of the voilation
of Documentation/SubmittingPatches section 2.2 in function
da830_evm_ui_expander_setup()

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>