Use fdt_overlay consistently in the identifiers and file/dir names.

Signed-off-by: Simon Glass <sjg@chromium.org>

As the overlays are sandbox specific, mark the whole test as depending
on sandbox.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>

Enable device tree overlay tests by default if unit tests are selected
and the runtime is configured via device tree.

Overlays have been mainlined in the device tree compiler so there is no
reason anymore to disable the tests by default.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

This adds a bunch of unit tests for the "fdt apply" command.

They've all been run successfully in the sandbox. However, as you still
require an out-of-tree dtc with overlay support, this is disabled by
default.

Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>