bionic(cm-12): Implement armv6 optimized strlen from glibc 2.18

Change-Id: Ief985c9ca08cb74d9d7e41d3a583e62699f745cf
bionic: cpu-features: enable LDREXD feature on ARMv6K

Change-Id: I6d30b8b65598512ca52280a6aa25342ba5af3491
Fix TLS register for thumb1

mrc is an arm opcode

Change-Id: Iaf1f7b957539c1f824f925ea574ff1955ff50d25
bionic: Fix atomic support for thumb1

ldrex and strex are arm opcodes

Change-Id: I41e0059d405998ea738ebcbf8cbb5716fee572d1