meta/conf: Start to populate autobuilder config fragments

meta/conf: Start to populate autobuilder config fragments

This populates the fragments directory with:

a) the default set of variables used in all autobuilder builds
b) the default resource related variables used in all autobuilder builds
c) three different multilib test configurations used by the autobuilder

The aim here is to start to make some of the autobuilder configuration more
visable and patchable by users, and to allow some test confiturations to
be user selectable if appropriate and needed for debugging.

The main aautobuilder fragment is probably not directly reusable by most
users, it contains the resource limits as used on the autobuilder itself. I
can see arguments both way for whether this should be included in OE-Core or not
but having an example of how we configure this is probably useful.

Not all configuration in the autobuilder is being moved, this set of variables
is just a basic starting point. Some variables may ultimately make more sense
being migrated elsewhere, perhaps updating the main defaults for poky or nodistro.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>