Add a sandbox reset controller compatible string
"sandbox,reset-ctl-fallback-only" that reuses the existing sandbox assert,
deassert, request, and free helpers but omits rst_reset. That forces
reset_reset() through the core assert / udelay / deassert fallback.
Extend the reset-ctl-test DT node with a fifth reset line named "fallback"
that points at the new provider, and add dm_test_reset_reset_fallback_path
which verifies sandbox_reset_get_count() stays zero (rst_reset is never
invoked) while the line ends deasserted after reset_reset().
This complements the existing rst_reset coverage on sandbox,reset-ctl and
matches the approach of using a separate controller to exercise the
fallback path in unit tests.
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/c1d40db6e2332a8b23ba842385b3f8c3d0290109.1779709539.git.michal.simek@amd.com