iommu/arm-smmu: Restore naming of driver parameter prefix

Extending the Arm SMMU driver to allow for modular builds changed
KBUILD_MODNAME to be "arm_smmu_mod" so that a single module could be
built from the multiple existing object files without the need to rename
any source files.

This inadvertently changed the name of the driver parameters, which may
lead to runtime issues if bootloaders are relying on the old names for
correctness (e.g. "arm-smmu.disable_bypass=0").

Although MODULE_PARAM_PREFIX can be overridden to restore the old naming
for builtin parameters, only the new name is matched by modprobe and so
loading the driver as a module would cause parameters specified on the
kernel command line to be ignored. Instead, rename "arm_smmu_mod" to
"arm_smmu". Whilst it's a bit of a bodge, this allows us to create a
single module without renaming any files and makes use of the fact that
underscores and hyphens can be used interchangeably in parameter names.

Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Reported-by: Li Yang <leoyang.li@nxp.com>
Fixes: cd221bd2 ("iommu/arm-smmu: Allow building as a module")
Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>