cmake: fix include directories to work with out-of-tree arch

Include directories for ${ARCH} is not specified correctly.
Several places in Zephyr, the include directories are specified as:
${ZEPHYR_BASE}/arch/${ARCH}/include
the correct line is:
${ARCH_DIR}/${ARCH}/include
to correctly support out of tree archs.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>