Introduce a Kconfig option (CONFIG_LIBMETAL_SRC_PATH) that allows us to
point to an external copy of libmetal.
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
With recent changes to libmetal we can now include and build it directly
as a zephyr library rather than doing a recursive make. We remove
ext/hal/libmetal.cmake as part of this change and introduce a Kconfig
option for libmetal.
This is a partial fix for issue #7673.
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>