[PATCH] revert the "remove kernel_flag" patch

[PATCH] revert the "remove kernel_flag" patch

With CONFIG_SMP=n, CONFIG_PREEMPT=y, CONFIG_DEBUG_SPINLOCK=y we get many
undefined refs to kernel_flag.

This is because spinlock debugging works on uniprocessor kernels now, and it
stores state inside the spinlock structure to do this.

Having working spinlock debugging on UP kernels seems more important than
saving four bytes, so...