of: unittest: Statically apply overlays using fdtoverlay

Now that fdtoverlay is part of the kernel build, start using it to test
the unitest overlays we have by applying them statically. Create two new
base files static_base_1.dts and static_base_2.dts which includes other
.dtsi files.

Some unittest overlays deliberately contain errors that unittest checks
for. These overlays will cause fdtoverlay to fail, and are thus not
included for static builds.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Tested-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/da6b4e6429aae2e7832a8be2ba2da473d449895b.1615354376.git.viresh.kumar@linaro.org