x86, earlyprintk: Add hsu early console for Intel Medfield platform

Intel Medfield platform has a high speed UART device, which
could act as a early console. To enable early printk of HSU
console, simply add "earlyprintk=hsu" in kernel command line.

Currently we put the code in the early_printk_mrst.c as it is
also for Intel MID platforms like the mrst early console

Signed-off-by: Feng Tang <feng.tang@intel.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Cc: greg@kroah.com
LKML-Reference: <1284361736-23011-5-git-send-email-feng.tang@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>