This commit removes the need for calling out ZEPHYR_MODULES via
MACHINEOVERRIDES. It uses west list to figure out what ZEPHYR_MODULES
are available and attaches them to -DZEPHYR_MODULES. Additional out of
tree modules may be added via ZEPHYR_EXTRA_MODULES.

Signed-off-by: Eilís Ní Fhlannagáin <elizabeth.flanagan@huawei.com>
Signed-off-by: Naveen Saini <naveen.kumar.saini@intel.com>