Patch from Manfred Spraul <manfred@colorfullife.com>

This enables spinlock debuggng on uniprocessor builds, under
CONFIG_DEBUG_SPINLOCK.

The reason I want this is that one day we'll need to pull out the debugging
support from the timer code which detects uninitialised timers.  And once
that has gone, uniprocessor developers and testers have no way of detecting
uninitialised timers - there will be mysterious deadlocks on SMP machines.
And there will surely be more uninitialised timers

The patch also removes the last pieces of the support for including
<asm/spinlock.h> directly.  Doesn't work since (IIRC) 2.3.x