[POWERPC] spufs: Add DEFINE_SPUFS_ATTRIBUTE()

This patch adds DEFINE_SPUFS_ATTRIBUTE(), a wrapper around
DEFINE_SIMPLE_ATTRIBUTE which does the specified locking for the get
routine for us.

Unfortunately we need two get routines (a locked and unlocked version) to
support the coredump code.  This hides one of those (the locked version)
inside the macro foo.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>