x86, realmode: Allow absolute pa_* symbols in the realmode code

Allow pa_* symbols to be absolute (outside any section) in the
realmode linker script.  Some versions of GNU ld are known to be
unhappy about symbols defined in a section that is otherwise empty.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-9-git-send-email-jarkko.sakkinen@intel.com