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>

arch/arm64/Makefile

@@ -62,6 +62,10 @@ zinstall install: vmlinux
 dtbs: scripts
 	$(Q)$(MAKE) $(build)=$(boot)/dts dtbs
 
+PHONY += vdso_install
+vdso_install:
+	$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso $@
+
 # We use MRPROPER_FILES and CLEAN_FILES now
 archclean:
 	$(Q)$(MAKE) $(clean)=$(boot)