asm-generic: use asm-generic/unaligned.h for most architectures

There are several architectures that just duplicate the contents
of asm-generic/unaligned.h, so change those over to use the
file directly, to make future modifications easier.

The exceptions are:

- arm32 sets HAVE_EFFICIENT_UNALIGNED_ACCESS, but wants the
  unaligned-struct version

- ppc64le disables HAVE_EFFICIENT_UNALIGNED_ACCESS but includes
  the access-ok version

- most m68k also uses the access-ok version without setting
  HAVE_EFFICIENT_UNALIGNED_ACCESS.

- sh4a has a custom inline asm version

- openrisc is the only one using the memmove version that
  generally leads to worse code.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>