crypto: vmx: Skip objtool from running on aesp8-ppc.o

With objtool enabled, below warnings are seen when trying to build:
  drivers/crypto/vmx/aesp8-ppc.o: warning: objtool: aes_p8_set_encrypt_key+0x44: unannotated intra-function call
  drivers/crypto/vmx/aesp8-ppc.o: warning: objtool: .text+0x2448: unannotated intra-function call
  drivers/crypto/vmx/aesp8-ppc.o: warning: objtool: .text+0x2d68: unannotated intra-function call

Skip objtool from running on drivers/crypto/vmx/aesp8-ppc.o file for the
following reasons:

- Since this file comes from OpenSSL, and since it is a perl file which
  generates a .S file, it may not be the best choice to make too many
  code changes to such files, unless absolutely necessary.

- As far as the objtool --mcount functionality is concerned, we do not
  have to run objtool on this file because there are no calls to
  _mcount().

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/20221114175754.1131267-6-sv@linux.ibm.com