pa.md (return): Revise comment for trivial return.

pa.md (return): Revise comment for trivial return.

        * pa.md (return): Revise comment for trivial return.
        (return_internal): Non-trivial return pattern for non-PIC code.
        (return_internal_pic): Non-trivial return pattern for PIC code.
        It uses the PIC register to ensure it is restored after
        function calls.
        (epilogue): Generate appropriate return for PIC and non-PIC code.

Co-Authored-By: Jeff Law <law@redhat.com>
From-SVN: r39345