fsl-kernel-localversion: Easy LOCALVERSION handling

fsl-kernel-localversion: Easy LOCALVERSION handling

This class allow for easy extending of kernel recipes to easy the
LOCALVERSION handling, allowing to reuse of code between different
kernel recipes

The following options are supported:

 SCMVERSION        Puts the Git hash in kernel local version
 LOCALVERSION      Value used in LOCALVERSION (default to '+fslc')

This about avoid code duplication among Layerscape and i.MX.

Change-Id: I3999dbdc2cb761063fe5f83dea65ddb14adec80c
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>