arm: Re-enable tmp105 test

The tmp105 test is currently not executed since the following
line in the Makefile overwrites the check-qtest-arm-y variable
instead of extending it.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-id: 1466760306-21849-1-git-send-email-thuth@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>