arm64/Makefile: provide vdso_install target

Provide a vdso_install target in the arm64 Makefile, as other architectures
with a vdso do.

Signed-off-by: Kyle McMartin <kyle@redhat.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-commit: 3c01742a8ac93a3abf9b099758db970410427afd
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>