lib/crc_kunit.c: add test and benchmark for crc7_be()

Wire up crc7_be() to crc_kunit.  Previously it had no test.

Link: https://lore.kernel.org/r/20250304223943.157493-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

lib/Kconfig.debug

@@ -2852,6 +2852,7 @@ config CRC_KUNIT_TEST
 	tristate "KUnit tests for CRC functions" if !KUNIT_ALL_TESTS
 	depends on KUNIT
 	default KUNIT_ALL_TESTS
+	select CRC7
 	select CRC16
 	select CRC_T10DIF
 	select CRC32