bionic: improve tls/atomic support for armv6

bionic_atomic_arm.h:
 * fix missing "+1" to enter THUMB mode in __ATOMIC_SWITCH_TO_THUMB

bionic_tls.h:
 * include __ATOMIC_SWITCH_TO_THUMB and __ATOMIC_SWITCH_TO_ARM
   macros
 * add thumb-1 support

Change-Id: I5d36e9ba55ffe14aa5918ac3f72436195dba401d