drm/vc4: tests: Retry pv-muxing tests when EDEADLK

drm/vc4: tests: Retry pv-muxing tests when EDEADLK

Some functions used by the HVS->PV muxing tests can return with EDEADLK,
meaning the entire sequence should be restarted. It's not a fatal error
and we should treat it as a recoverable error, and recover, instead of
failing the test like we currently do.

Fixes: 76ec18dc5afa ("drm/vc4: tests: Add unit test suite for the PV muxing")
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Link: https://lore.kernel.org/r/20250403-drm-vc4-kunit-failures-v2-4-e09195cc8840@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>