platform/chrome: Move mfd/cros_ec_lpc* includes to drivers/platform.

The cros-ec-lpc driver lives in drivers/platform because is platform
specific, however there are two includes (cros_ec_lpc_mec.h and
cros_ec_lpc_reg.h) that lives in include/linux/mfd. These two includes
are only used for the platform driver and are not really related to the
MFD subsystem, so move the includes from include/linux/mfd to
drivers/platform/chrome.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Benson Leung <bleung@chromium.org>