linux-common: Use IMAGE_VERSION_SUFFIX instead of DATETIME
linux-common: Use IMAGE_VERSION_SUFFIX instead of DATETIME

With thud name variables (e.g. IMAGE_NAME) use a new IMAGE_VERSION_SUFFIX
variable instead of DATETIME.

See section: 25.14.7. Image/Kernel Artifact Naming Changes
in manual:   https://www.yoctoproject.org/docs/2.6/mega-manual/mega-manual.html

Signed-off-by: Norbert Wesp <6da95d5bf7a9ae873d28e5fc932fdf5af58a5861@phytec.de>
Signed-off-by: Stefan Müller-Klieser <a3e08e35e4a42be768e7d0e76ae1ba321c2a66dd@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