iMX6: Use hard-float ABI

The toolchain and image for iMX6 used in the CI are build with hard-float ABI,
while the default mkspec for iMX6 uses soft-float.

Change-Id: Ib5c6a95bc5502595b221ff502b8756d7b86c4ec2
Reviewed-by: Sergio Ahumada <sahumada@blackberry.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>