toolchain.inc: Update help text, Add TODO.

- Update the help text to be more informative.
- Add todo about IASL - we shouldn't require it if the build doesn't
use it.

Change-Id: Iffeb94f78c1ae7535a8a7b9b0b9f1728301a42b3
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12680
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed