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/gpio/gpio-aspeed.c

@@ -611,16 +611,16 @@ static int aspeed_gpio_set_type(struct irq_data *d, unsigned int type)
 	switch (type & IRQ_TYPE_SENSE_MASK) {
 	case IRQ_TYPE_EDGE_BOTH:
 		type2 |= bit;
-		/* fall through */
+		fallthrough;
 	case IRQ_TYPE_EDGE_RISING:
 		type0 |= bit;
-		/* fall through */
+		fallthrough;
 	case IRQ_TYPE_EDGE_FALLING:
 		handler = handle_edge_irq;
 		break;
 	case IRQ_TYPE_LEVEL_HIGH:
 		type0 |= bit;
-		/* fall through */
+		fallthrough;
 	case IRQ_TYPE_LEVEL_LOW:
 		type1 |= bit;
 		handler = handle_level_irq;