ACPI: handle invalid ACPI SLIT table

This is a SLIT sanity checking patch.  It moves slit_valid() function to
generic ACPI code and does sanity checking for both x86 and ia64.  It sets up
node_distance with LOCAL_DISTANCE and REMOTE_DISTANCE when hitting invalid
SLIT table on ia64.  It also cleans up unused variable localities in
acpi_parse_slit() on x86.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>