mtd: move all flash categories inside MTD submenu

There is no reason to have NAND, SPI flashes and UBI sections outside of
the MTD submenu in Kconfig.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>

drivers/mtd/Kconfig

@@ -59,10 +59,10 @@ config RENESAS_RPC_HF
 	  This enables access to Hyperflash memory through the Renesas
 	  RCar Gen3 RPC controller.
 
-endmenu
-
 source "drivers/mtd/nand/Kconfig"
 
 source "drivers/mtd/spi/Kconfig"
 
 source "drivers/mtd/ubi/Kconfig"
+
+endmenu