powerpc/swsusp: Include suspend.h to silence sparse warnings

Sparse emits two symbol not declared warnings for swsusp.c. The two
functions, save_processor_state() and restore_processor_state() are
declared already in suspend.h, so include it.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>