mfd: smsc: Add support for smsc gpio io/keypad driver

smsc ece1099 is a keyboard scan or gpio expansion device.
The patch create keypad and gpio expander child for this
multi function smsc driver.

Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>