xtensa: xcc workarounds

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: fix asm constraints unsupported by xcc

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: fix xcc build failure due to weird section names

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