revocable: Add KUnit test for provider lifetime races

revocable: Add KUnit test for provider lifetime races

Add a test to verify that revocable_alloc() correctly handles race
conditions where the provider is being released.

The test covers three scenarios:
1. Allocating from a NULL provider.
2. Allocating from a provider that has been detached (pointer is NULL).
3. Allocating from a provider that is in the process of destruction
   (refcount is 0), simulating a race between revocable_alloc() and
   revocable_provider_release().

A way to run the test:
$ ./tools/testing/kunit/kunit.py run \
	--kconfig_add CONFIG_REVOCABLE_KUNIT_TEST=y \
	--kconfig_add CONFIG_PROVE_LOCKING=y \
	--kconfig_add CONFIG_DEBUG_KERNEL=y \
	--kconfig_add CONFIG_DEBUG_INFO=y \
	--kconfig_add CONFIG_DEBUG_INFO_DWARF5=y \
	--kconfig_add CONFIG_KASAN=y \
	--kconfig_add CONFIG_DETECT_HUNG_TASK=y \
	--kconfig_add CONFIG_DEFAULT_HUNG_TASK_TIMEOUT="10" \
	--arch=x86_64 --raw_output=all \
	revocable_test

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://patch.msgid.link/20260129143733.45618-3-tzungbi@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>