linux-wrs: implement BSP bootstrapping via fallback branches
When creating a new BSP there isn't always an upstream branch
to validate SRCREVs against. Therefore, creating a new BSP
required extra manipulations of the git repository, even though
the branch for the build would be dynamically created.
To fix this, provide a fallback to the 'standard' branch if
WRMACHINE is not assigned a specific value for the given MACHINE.
The fallback saved in KBRANCH, and represents the branch that
we should build, even if no fallback is required. Some substeps
of the recipe have been updated to use KBRANCH rather than
enforcing MACHINE-KERNELTYPE.
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
