i#1551 Port DynamoRIO to ARM: add new TLS typ TLS_TYPE_SWAP

There is only one thread pointer (register) is available on ARM Linux.
In order to support DR TLS reference in normal C code, we steal an app TLS
slot in the DR context and restore its app value on entering code cache.
- add TLS_TYPE_SWAP
- add TLS_SWAP_SLOT_OFFSET
- add get_app_tls_swap_slot_addr on ARM
- implement tls_thread_init and tls_thread_free for ARM
- rename is_thread_register_initialized to is_thread_tls_initialized
- adjust default options in ARM

Review-URL: https://codereview.appspot.com/188840043