linux-*: Rework LOCALVERSION depending on SRCBRANCH

LOCALVERSION is used in FSL Community BSP Release Notes and should highlight
which are the _release version_ for that particular provider.

In addition LOCALVERSION makes it easy to track where the binary running on a
target is from.

Both reasons make LOCALVERSION a very important information.

The overall rule is that LOCALVERSION would point to SRCBRANCH, unless in a
case of explicit exception.

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>