libs/libc/pthread/pthread_spinlock.c: Resolve several TODO issues by accessing up_testset() via the boardctl() interface rather than attempting to call it directly.
configs/boardctl.c, include/sys/boardctl.h: Add access to architecture-specific up_testset() via boardctl().
arch/Kconfig's, sched/Kconfig, and include/nuttx/spinlock.h: Spinlocks are not available unless the architecture supports the up_testset() operation.