ACPICA: Dump table header - suppress output of non-printable characters

Function acpi_tb_print_table_header. Some ACPI tables contain
non-printable characters in one of the string fields of the the
header - Signature, OemId, OemTableId, or CompilerId. Invalid
characters are replaced by '?'. ACPICA BZ 788.

http://acpica.org/bugzilla/show_bug.cgi?id=788

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>