SFI: add capability to parse ACPI tables

Extend SFI to access standard ACPI tables.
(eg. the PCI MCFG) using sfi_acpi_table_parse().

Note that this is _not_ a hybrid ACPI + SFI mode.
The platform boots in either ACPI mode or SFI mode.

SFI runs only with acpi_disabled=1, which can be set
at build-time via CONFIG_ACPI=n, or at boot time by
the failure to find ACPI platform support.

So this extension simply allows SFI-platforms to
re-use existing standard table formats that happen to
be defined to live in ACPI envelopes.

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