lib/crc: tests: Add a .kunitconfig file

Add a .kunitconfig file to the lib/crc/ directory so that the CRC
library tests can be run more easily using kunit.py.  Example with UML:

    tools/testing/kunit/kunit.py run --kunitconfig=lib/crc

Example with QEMU:

    tools/testing/kunit/kunit.py run --kunitconfig=lib/crc --arch=arm64 --make_options LLVM=1

Link: https://lore.kernel.org/r/20260306033557.250499-4-ebiggers@kernel.org


Signed-off-by: Eric Biggers <ebiggers@kernel.org>