iommu: Improve map/unmap sanity checks

The current checks for the __IOMMU_DOMAIN_PAGING capability seem a
bit stifled, since it is quite likely now that a non-paging domain
won't have a pgsize_bitmap and/or mapping ops, and thus get caught
by the earlier condition anyway. Swap them around to test the more
fundamental condition first, then we can reasonably also upgrade
the other to a WARN_ON, since if a driver does ever expose a paging
domain without the means to actually page, it's clearly very broken.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/524db1ec0139c964d26928a6a264945aa66d010c.1694525662.git.robin.murphy@arm.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>