cmake: armfvp: Improve the FVP version check

Print a warning message on 'west build -t run', if the FVP does not meet
the minimal requirement. The check acts as a reminder instead of an
entrance guard. So, the check won't stop executing the FVP program.

Signed-off-by: Jaxson Han <jaxson.han@arm.com>
(cherry picked from commit 1a682680)