binder: Scaffolding for binder_alloc KUnit tests

Add setup and teardown for testing binder allocator code with KUnit.
Include minimal test cases to verify that tests are initialized
correctly.

Tested-by: Rae Moar <rmoar@google.com>
Signed-off-by: Tiffany Yang <ynaffit@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20250714185321.2417234-5-ynaffit@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>