mtd: bcm47xxpart: limit scanned flash area on BCM47XX (MIPS) only

We allowed using bcm47xxpart on BCM5301X arch with commit:
9e3afa5f ("mtd: bcm47xxpart: allow enabling on ARCH_BCM_5301X")

BCM5301X devices may contain some partitions in higher memory, e.g.
Netgear R8000 has board_data at 0x2600000. To detect them we should
use size limit on MIPS only.
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/bcm47xxpart.c

@@ -118,8 +118,8 @@ static int bcm47xxpart_parse(struct mtd_info *master,
 	/* Parse block by block looking for magics */
 	for (offset = 0; offset <= master->size - blocksize;
 	     offset += blocksize) {
-		/* Nothing more in higher memory */
-		if (offset >= 0x2000000)
+		/* Nothing more in higher memory on BCM47XX (MIPS) */
+		if (config_enabled(CONFIG_BCM47XX) && offset >= 0x2000000)
 			break;
 
 		if (curr_part >= BCM47XXPART_MAX_PARTS) {