iommu: Correct iommu_map / iommu_unmap prototypes

Commit 7d3002cc ("iommu/core: split mapping to page sizes as supported
by the hardware") replaced 'int gfp_order' with a 'size_t size' of
iommu_map / iommu_unmap function arguments, but missed the function
prototypes for the disabled CONFIG_IOMMU_API case, let's correct them
for consistency.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>