recipes-kernel: Set DEFAULT_PREFERENCE to "-1" for 4.14.y
recipes-kernel: Set DEFAULT_PREFERENCE to "-1" for 4.14.y

bitbake will prefer 4.14.y because: y > number.
Setting the DEFAULT_PREFERENCE to "-1" makes the recipe unlikely to be
used unless it is explicitly referenced.

Signed-off-by: Wadim Egorov <f42ccee66aacafbe10be12a603629f53944208c9@phytec.de>

PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec