SFI: create linux/sfi.h

include/linux/include/sfi.h defines everything that customers
of SFI need to know in order to use the SFI suport in the kernel.

The primary API is sfi_table_parse(), where a driver or another part
of the kernel can supply a handler to parse the named table.

sfi.h also includes the currently defined table signatures and table
formats.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>