iommu/fsl: Fix PAMU window size check.

is_power_of_2 requires an unsigned long parameter which would
lead to truncation of 64 bit values on 32 bit architectures.

__ffs also expects an unsigned long parameter thus won't work
for 64 bit values on 32 bit architectures.

Signed-off-by: Varun Sethi <Varun.Sethi@freescale.com>
Tested-by: Emil Medve <Emilian.Medve@Freescale.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>