BSPs are built from a particular branch of the kernel repository
which is specfied via the mapping of MACHINE to KMACHINE. Unless
a global branch is being forced (like libc headers), KMACHINE
is an override on a per machine basis.
Because KMACHINE is typically override we must first try the
most specific variant KMACHINE_<machine> and if that is undefined
look for a fallack default. This allows any combination of
variables to work (and at the time the anonymous python
executes) safely and get us a properly defined branch for the
fetcher and build.
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
