Input: elants_i2c - wire up regulator support

Elan touchscreen controllers use two power supplies, vcc33 and vccio,
and we need to enable them before trying to access the device. On X86
firmware usually does this, but on ARM it is usually left to the kernel.

Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Reviewed-by: Scott Liu <scott.liu@emc.com.tw>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>