Make master compatible with the new syntax for overrides

Make master compatible with the new syntax for overrides

Upstream YP introduced a new syntax for overrides
e.g.:
SRC_URI_qemux86 = file://somefile

becomes:

SRC_URI:qemux86 = file://somefile

While this change is only *required* for the upcoming YP 3.4 'honister' release,
YP 3.1 'dunfell' got extended to allow the new syntax to be parsed.
Unfortunately 3.1.10 did not include this, yet.
We do move past 3.1.10 by 3 commits here to simplify our work on master and next.

See: https://docs.yoctoproject.org/migration-guides/migration-3.4.html?highlight=overrides#override-syntax-changes

Bug-AGL: SPEC-4052
Signed-off-by: Jan-Simon Möller <jsmoeller@linuxfoundation.org>
Change-Id: Icc342275500915e38d7ddf6d09db21297539a3c1