S/390: Move binary start to 16M.

S/390: Move binary start to 16M.

Turned out that by moving the binary start to 256M I've hit a case with
potentially a lot of aliasing in the branch target buffer between
binaries and shared libs.  So moving on.

Tested on s390x. No regressions.

ld/ChangeLog:

2016-10-10  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* emulparams/elf64_s390.sh: Move binary start to 16M.
	* testsuite/ld-s390/tlsbin_64.dd: Adjust testcases accordingly.
	* testsuite/ld-s390/tlsbin_64.rd: Likewise.