CI: Azure: Correctly skip semihosting tests on vexpress_fvp

CI: Azure: Correctly skip semihosting tests on vexpress_fvp

In commit d75998b476de ("Docker, CI: Add vexpress_fvp /
vexpress_fvp_bloblist support") we specifically disable the semihosting
tests on FVP using platforms due to upstream issues. With commit
7ffa20af30dd ("Merge patch series "fs: regression-safe load <iface> for
null_dev_desc_ok fstypes"") we add a new test that was not caught with
"hostfs" because it's a semihosting test. Update the logic in our
pipeline to skip all semihosting tests.

Signed-off-by: Tom Rini <trini@konsulko.com>