fastboot: Implement NAND backend

So far the fastboot code was only supporting MMC-backed devices for its
flashing operations (flash and erase).

Add a storage backend for NAND-backed devices.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
diff --git a/common/Makefile b/common/Makefile
index d986cde..4c1b2f0 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -276,10 +276,15 @@
 obj-y += stdio.o
 
 # This option is not just y/n - it can have a numeric value
-ifdef CONFIG_FASTBOOT_FLASH_MMC_DEV
+ifdef CONFIG_FASTBOOT_FLASH
 obj-y += aboot.o
+ifdef CONFIG_FASTBOOT_FLASH_MMC_DEV
 obj-y += fb_mmc.o
 endif
+ifdef CONFIG_FASTBOOT_FLASH_NAND_DEV
+obj-y += fb_nand.o
+endif
+endif
 
 obj-$(CONFIG_CMD_BLOB) += cmd_blob.o