kernel/mempool: Spinlockify
kernel/mempool: Spinlockify

Really the locking in this file is vestigial.  It only exists because
the scheduler's _unpend_all() call to wake up everyone waiting on a
wait_q is unsynchronized, because it was written to assume
irq_lock-style-locking.  It would be cleaner to put that locking into
the wait_q itself and/or use the scheduler's subsystem lock.  But it's
not clear there's any performance benefit, so let's stick with the
more easily verifiable change first.

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

Vudentz/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,explora26/zephyr,galak/zephyr,ldts/zephyr,Vudentz/zephyr,ldts/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,finikorg/zephyr,explora26/zephyr,explora26/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,ldts/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,ldts/zephyr,finikorg/zephyr