ACPICA: Fix regression in FADT revision checks

	commit 64b3db22 (2.6.39),
"Remove use of unreliable FADT revision field" causes regression
for old P4 systems because now cst_control and other fields are
not reset to 0.

	The effect is that acpi_processor_power_init will notice
cst_control != 0 and a write to CST_CNT register is performed
that should not happen. As result, the system oopses after the
"No _CST, giving up" message, sometimes in acpi_ns_internalize_name,
sometimes in acpi_ns_get_type, usually at random places. May be
during migration to CPU 1 in acpi_processor_get_throttling.

	Every one of these settings help to avoid this problem:
 - acpi=off
 - processor.nocst=1
 - maxcpus=1

	The fix is to update acpi_gbl_FADT.header.length after
the original value is used to check for old revisions.

https://bugzilla.kernel.org/show_bug.cgi?id=42700
https://bugzilla.redhat.com/show_bug.cgi?id=727865



Signed-off-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>