smbios: Use integer signature instead of string signature

smbios: Use integer signature instead of string signature

Change the smbios structure to use a 4 byte u32 signature field
instead of a 4 byte character string field.  In practice, this allows
the compiler to place the signature in the initialize code segment and
thus makes it less likely the signature would be found in the
f-segment.  (If the smbios signature is found in the f-segment it can
confuse some table scans.)

Reviewed-by: Bruce Rogers <brogers@suse.com>
Tested-by: Bruce Rogers <brogers@suse.com>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>