powerpc: use linux/unaligned/le_struct.h on LE power7

Little-endian POWER7 kernels disable
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS because that is not supported on
the hardware, but the kernel still uses direct load/store for explicti
get_unaligned()/put_unaligned().

I assume this is a mistake that leads to power7 having to trap and fix
up all these unaligned accesses at a noticeable performance cost.

The fix is completely trivial, just remove the file and use the
generic version that gets it right.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>