treewide: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/perf/arm-ccn.c

@@ -1404,7 +1404,7 @@ static int arm_ccn_init_nodes(struct arm_ccn *ccn, int region,
 		break;
 	case CCN_TYPE_SBAS:
 		ccn->sbas_present = 1;
-		/* Fall-through */
+		fallthrough;
 	default:
 		component = &ccn->node[id];
 		break;