Merge tag 'xtensa-20260422' of https://github.com/jcmvbkbc/linux-xtensa

Pull Xtensa updates from Max Filippov:

 - use register_sys_off_handler(SYS_OFF_MODE_RESTART) instead of
   the deprecated register_restart_handler()

 - drop custom ucontext.h and reuse asm-generic ucontext.h

* tag 'xtensa-20260422' of https://github.com/jcmvbkbc/linux-xtensa:
  xtensa: uapi: Reuse asm-generic ucontext.h
  xtensa: xtfpga: Use register_sys_off_handler(SYS_OFF_MODE_RESTART)
  xtensa: xt2000: Use register_sys_off_handler(SYS_OFF_MODE_RESTART)
  xtensa: ISS: Use register_sys_off_handler(SYS_OFF_MODE_RESTART)