drivers: gpio: omap: add support for parsing additional gpio parameters

With DM_GPIO, gpio parameters like ACTIVE_(LOW/HIGH) are to be
parsed in xlate gpio drivers-ops. Since xlate is not implemented
in omap_gpio driver, the driver considers all gpio to be
ACTIVE_HIGH which is the default case and fails to return actual
gpio status for ACTIVE_LOW gpios. So adding .xlate ops to
omap_gpio.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>