i40e/base: grab NVM devstarter version instead of image version

i40e/base: grab NVM devstarter version instead of image version

The NVM image version has useful data but it is a per image version,
and every image can have a different one. While for the dev starter
version, all the images for release will have the same version. So
it would be better to use dev starter version number.

Test report: http://www.dpdk.org/ml/archives/dev/2015-May/017384.html

Signed-off-by: Helin Zhang <helin.zhang@intel.com>
Acked-by: Jijiang Liu <jijiang.liu@intel.com>
Tested-by: Min Cao <min.cao@intel.com>