powerpc/mm: check for irq disabled() only if DEBUG_VM is enabled

powerpc/mm: check for irq disabled() only if DEBUG_VM is enabled

We don't need to check this always.  The idea here is to capture the
wrong usage of find_linux_pte_or_hugepte and we can do that by
occasionally running with DEBUG_VM enabled.

Link: http://lkml.kernel.org/r/1464692688-6612-2-git-send-email-aneesh.kumar@linux.vnet.ibm.com
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>