Analogous to ACPI's /sys/firmware/acpi/tables/...

create /sys/firmware/sfi/tables/

The tables are primariy for the kernel,
but sometimes it is useful for user-space to be
able to read them.
Signed-off-by: NFeng Tang <feng.tang@intel.com>
Signed-off-by: NLen Brown <len.brown@intel.com>