powerpc/cpm1: Fix race condition in CPM1 GPIO library.

The CPM1 GPIO library code uses the non thread-safe clrbits32/setbits32
macros. This patch protects them with a spinlock.

Based on the CPM2 patch from Laurent Pinchart <laurentp@cse-semaphore.com>,
commit 639d6445.

Signed-off-by: Jochen Friedrich <jochen@scram.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>