target/xtensa: break circular register dependencies

target/xtensa: break circular register dependencies

Currently topologic opcode sorting stops at the first detected
dependency loop. Introduce struct opcode_arg_copy that describes
temporary register copy. Scan remaining opcodes searching for
dependencies that can be broken, break them by introducing temporary
register copies and record them in an array. In case of success
create local temporaries and initialize them with current register
values. Share single temporary copy between all register users. Delete
temporaries after translation.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>