XT_* macros are defined in xtensa HAL headers as xcc intrinsics. gcc
does not have any of these intrinsics. Replace XT_* macros with inline
assembly or provide gcc-compatible definitions.
Change-Id: If823ea8a7898a11a3a8363b17efdba27dee4c6a4
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>