Don't run pr27228 test for hppa

As the comment says, hppa doesn't support use of BFD_RELOC_* in
.reloc directives.  Using xfail can result in a spurious XPASS result
as BFD_RELOC values change.

	* testsuite/gas/elf/pr27228.d: Change xfail to notarget for hppa.