powerpc/64s: Remove support for ELFv1 little endian userspace

ELFv2 was introduced together with little-endian. ELFv1 with LE has
never been a thing. The GNU toolchain can create such a beast, but
anyone doing that is a maniac who needs to be stopped so I consider
this patch a feature.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230606093832.199712-5-npiggin@gmail.com