fsl-eula-unpack: add FSL_EULA_FILE to vardepsexclude
FSL_EULA_FILE is defined with :=, which means it contains a full absolute path
to the layer directory. If this is allowed to make it into the task checksum,
it becomes impossible to use the shared states for these recipes without
having meta-fsl-arm in the exact same path in the filesystem it was in when
the sstate archives were created. Add FSL_EULA_FILE to
do_unpack[vardepsexclude].
Signed-off-by: Christopher Larson <kergoth@gmail.com>
