serial: pch_uart: support new device ML7213

Support ML7213 device of OKI SEMICONDUCTOR.
ML7213 is companion chip of Intel Atom E6xx series for IVI(In-Vehicle Infotainment).
ML7213 is completely compatible for Intel EG20T PCH.

Signed-off-by: Tomoya MORINAGA <tomoya-linux@dsn.okisemi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>