zephyr: Make Zephyr int types deprecated by default

As the int types defined in include/zephyr/types.h are typdef's we
utilize a Kconfig option (LEGACY_ZEPHYR_INT_TYPES) to enable/disable
the support for them.  By default to LEGACY_ZEPHYR_INT_TYPES not
being enabled and add an explicit test to ensure the types continue to
function until removed in the future.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>