sandbox: correct posix_types.h define

arch/arm/include/asm/posix_types.h and
arch/sandbox/include/asm/posix_types.h should use different defines.

Add SPDX header.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

sandbox: Add architecture header files

This adds required header files for the sandbox architecture, and a basic
description of what sandbox is (README.sandbox).

Signed-off-by: Simon Glass <sjg@chromium.org>

sandbox: Add architecture header files

This adds required header files for the sandbox architecture, and a basic
description of what sandbox is (README.sandbox).

Signed-off-by: Simon Glass <sjg@chromium.org>