Currently, the kernel won't compile for SMP ppc32 if preempt is
enabled.  This patch adds suitable read_can_lock and write_can_lock
definitions.

This patch also adds a real _raw_read_trylock (inline and out-of-line
versions), changes the rwlock->lock field to a signed int, which is
what it really was all along, and cleans up the out-of-line rwlock
code in arch/ppc/lib/locks.c.  It removes the debug fields from the
rwlock struct because we were never using them, even with
CONFIG_DEBUG_SPINLOCK set.

I have compile and boot tested this with the four combinations of
CONFIG_DEBUG_SPINLOCKS on and off, and CONFIG_PREEMPT on and off.
Please put this patch into 2.6.11 so that 2.6.11 will work for
ppc32 with CONFIG_SMP and CONFIG_PREEMPT.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>