build: make zephyrmake exposed with V=1

Remove extra @ which would always silence output from zephyrmake.  Every
instance of zephyrmake is prefixed with a $(Q) so V=1 will expose them

Change-Id: I8e622cc2175f645897ac78d607486d37c0af1618
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>