powerpc64: Set PPC64_ELF_ABI_v[1|2] macros to 1

Set macros to 1 so that they can be used with __is_defined().

Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/abad4868416ddfd42893f99c0cad8e5faf998095.1644834730.git.naveen.n.rao@linux.vnet.ibm.com