iommu/arm-smmu: Make arm-smmu explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/iommu/Kconfig:config ARM_SMMU
drivers/iommu/Kconfig:  bool "ARM Ltd. System MMU (SMMU) Support"

...meaning that it currently is not being built as a module by anyone.

Lets remove the modular code that is essentially orphaned, so that
when reading the driver there is no doubt it is builtin-only.

Since module_platform_driver() uses the same init level priority as
builtin_platform_driver() the init ordering remains unchanged with
this commit.

We explicitly disallow a driver unbind, since that doesn't have a
sensible use case anyway, but unlike most drivers, we can't delete the
function tied to the ".remove" field.  This is because as of commit
7aa8619a

 ("iommu/arm-smmu-v3: Implement shutdown method") the
.remove function was given a one line wrapper and re-used to provide a
.shutdown service.  So we delete the wrapper and re-name the function
from remove to shutdown.

We add a moduleparam.h include since the file does actually declare
some module parameters, and leaving them as such is the easiest way
currently to remain backwards compatible with existing use cases.

We also delete the MODULE_LICENSE tag etc. since all that information
is already contained at the top of the file in the comments.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Nate Watterson <nwatters@codeaurora.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: iommu@lists.linux-foundation.org
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>