x86, mrst: Add platform timer info parsing code

Moorestown platform timer information is obtained from SFI FW tables.
This patch parses SFI table then assign the irq information to mp_irqs.

Signed-off-by: Jacob Pan <jacob.jun.pan@intel.com>
LKML-Reference: <43F901BD926A4E43B106BF17856F07559FB80D0B@orsmsx508.amr.corp.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>