Don't touch r11 in __tls_get_addr stub

Don't touch r11 in __tls_get_addr stub

This modifies the special __tls_get_addr stub that checks for a
tlsdesc style __tls_index entry and returns early.  Not using r11
isn't much benefit at the moment but a followup patch will preserve
regs around the first call to __tls_get_addr when the __tls_index
entry isn't yet set up for an early return.

bfd/
	* elf64-ppc.c (LD_R11_0R3, CMPDI_R11_0, STD_R11_0R1, LD_R11_0R1),
	(MTLR_R11): Don't define.
	(LD_R0_0R3, CMPDI_R0_0): Define.
	(build_tls_get_addr_stub): Don't use r11 in stub.
ld/
	* testsuite/ld-powerpc/tlsexe.d: Match new __tls_get_addr stub.
	* testsuite/ld-powerpc/tlsexeno.d: Likewise.
	* testsuite/ld-powerpc/tlsexetoc.d: Likewise.
	* testsuite/ld-powerpc/tlsexetocno.d: Likewise.
	* testsuite/ld-powerpc/tlsopt5.d: Likewise.