powerpc/vdso: Skip objtool from running on VDSO files

Do not run objtool on VDSO files, by using OBJECT_FILES_NON_STANDARD.

Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221114175754.1131267-8-sv@linux.ibm.com