iommu/vt-d: Cleanup after delegating DMA domain to generic iommu

[No functional changes]

1. Starting with commit df4f3c60 ("iommu/vt-d: Remove static identity
map code") there are no callers for iommu_prepare_rmrr_dev() but the
implementation of the function still exists, so remove it. Also, as a
ripple effect remove get_domain_for_dev() and iommu_prepare_identity_map()
because they aren't being used either.

2. Remove extra new line in couple of places.

Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>