powerpc: Always select HAVE_EFFICIENT_UNALIGNED_ACCESS

powerpc: Always select HAVE_EFFICIENT_UNALIGNED_ACCESS

Currently powerpc selects HAVE_EFFICIENT_UNALIGNED_ACCESS in all cases
but one. The exception is if the kernel is being built little endian and
explicitly targeted for Power7.

The combination of Power7 and little endian was never commercially
supported, or widely used. It was only ever possible on bare metal
machines, using unofficial firmware, or in qemu guests hosted on those
machines.

The bare metal firmware support for Power7 was removed in 2019, see
skiboot commit 16b7ae64 ("Remove POWER7 and POWER7+ support").

Little endian kernel builds were switched to target Power8 or later in
2018, in commit e6a7e66950d6 ("powerpc/64: Add GENERIC_CPU support for
little endian"). Since then it's only been possible to boot a Power7/LE
kernel by explicitly building for Power7.

So drop the exception and always select HAVE_EFFICIENT_UNALIGNED_ACCESS.
If anyone does still have a Power7/LE machine it should hopefully
continue to boot, just with some performance penality, and if not they
can report a bug.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220916131523.319123-1-mpe@ellerman.id.au