Add the core support needed by the ep93xx matrix keypad driver.

The keypad driver unfortunately was merged early and the core
support is missing.  The clkdev support has been resolved and
is now merged.  This adds the platform device to the ep93xx
core and supplies the functions needed to acquire/free the gpio
pins and actually enable/disable the controller peripheral.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: NRyan Mallon <ryan@bluewatersys.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>