xtensa: don't modify call* patterns, use is_leaf

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: adjust register class definitions at runtime

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Turn RETURN_ADDR_IN_PREVIOUS_FRAME into C expression

This allows a target to support both windowed and non-windowed ABI.

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