s390: Do not emit orphaned GOT entry for TLS IE to LE transition

Commit 69fc87f180bf introduced TLS support for s390 32-bit and 64-bit.
It defined GOT_TLS_IE_NLT in both elf32-s390.c and elf64-s390.c, but
erroneously assigned it the same value as GOT_TLS_IE in elf64-s390.c.
As a consequence the linker for s390 64-bit erroneously emitted an
orphaned GOT entry when performing TLS Initial Exec (IE) to Local
Exec (LE) transition optimization.

Correct the value of GOT_TLS_IE_NLT in elf64-s390.c.  This causes the
liker to actually optimize away the GOT entry when performing IE to LE
transition.  While at it add a comment that the suffix NLT denotes
"no literal (pool entry)".

Found while inspecting and cleaning up differences between elf32-s390.c
and elf64-s390.c.

bfd/
	* elf32-s390.c (GOT_TLS_IE_NLT): Add comment that NLT denotes
	no literal pool entry.
	* elf64-s390.c (GOT_TLS_IE_NLT): Likewise.  Correct value.

ld/testsuite/
	* ld-s390/tlsbin_64.dd: Adjust expected test results.
	* ld-s390/tlsbin_64.sd: Likewise.

Fixes: 69fc87f180bf
Signed-off-by: Jens Remus <jremus@linux.ibm.com>