mtd: move NAND files into a raw/ subdirectory

NAND flavors, like serial and parallel, have a lot in common and would
benefit to share code. Let's move raw (parallel) NAND specific code in a
raw/ subdirectory, to ease the addition of a core file in nand/ and the
introduction of a spi/ subdirectory specific to SPI NANDs.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
diff --git a/drivers/mtd/Makefile b/drivers/mtd/Makefile
index 9cec065..cdf5152 100644
--- a/drivers/mtd/Makefile
+++ b/drivers/mtd/Makefile
@@ -18,3 +18,5 @@
 obj-$(CONFIG_ST_SMI) += st_smi.o
 obj-$(CONFIG_STM32_FLASH) += stm32_flash.o
 obj-$(CONFIG_RENESAS_RPC_HF) += renesas_rpc_hf.o
+
+obj-y += nand/