serial: reduce include platform file for marvell chip

Build pass with following config:
dkb_config
aspenite_config
edminiv2_config
openrd_ultimate_config
sheevaplug_config
mv88f6281gtw_ge_config
rd6281a_config
guruplug_config
km_kirkwood_config

Signed-off-by: Lei Wen <leiwen@marvell.com>
Acked-by: Wolfgang Denk <wd@denx.de>