xtensa: asm2 needs to honor thread preemption
xtensa: asm2 needs to honor thread preemption

Forgot to check the thread preemption status when fetching the stack
to restore.

Signed-off-by: Andy Ross <c70f9a6bf6ee0cd69c8af4ce5e6b131945769315@intel.com>

zephyriot/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,explora26/zephyr,finikorg/zephyr,nashif/zephyr,mbolivar/zephyr,ldts/zephyr,kraj/zephyr,nashif/zephyr,Vudentz/zephyr,ldts/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,galak/zephyr,punitvara/zephyr,galak/zephyr,punitvara/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyriot/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,zephyriot/zephyr,kraj/zephyr,explora26/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,zephyriot/zephyr,explora26/zephyr,Vudentz/zephyr,finikorg/zephyr,kraj/zephyr,nashif/zephyr,punitvara/zephyr,mbolivar/zephyr,explora26/zephyr,punitvara/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,kraj/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,ldts/zephyr,mbolivar/zephyr,mbolivar/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr