platform/chrome: Make depends on MFD_CROS_EC instead CROS_EC_PROTO

The ChromeOS EC LPC and chardev drivers depend on CROS_EC_PROTO but
MFD_CROS_EC select CROS_EC_PROTO instead. Mixing select and depends
on is bad practice as it may lead to circular Kconfig dependencies.

Since the platform devices that are matched with these drivers are
registered by the ChromeOS EC mfd driver, they really depend on
MFD_CROS_EC. And because this config option selects CROS_EC_PROTO,
that dependency is met as well. So make the drivers to depend on
MFD_CROS_EC instead of CROS_EC_PROTO.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Olof Johansson <olof@lixom.net>