mtd: nand: Allow MTD_NAND_BRCMNAND to be selected for ARM64

The BRCM NAND driver can be re-used for Broadcom ARM64 SoCs hence
this patch updates Kconfig to allow selection of MTD_NAND_BRCMNAND
for ARM64.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Vikram Prakash <vikramp@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Pramod KUMAR <pramodku@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>