Fix 'make headers_check' on m32r

> asm-m32r/page.h requires asm-generic/memory_model.h, which does not exist
> asm-m32r/ptrace.h requires asm/m32r.h, which does not exist
> asm-m32r/signal.h requires linux/linkage.h, which does not exist
> asm-m32r/unistd.h requires asm/syscall.h, which does not exist
> asm-m32r/user.h requires asm/processor.h, which does not exist

Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>