MLK-9851 mtd: Change the mtd device driver build order for mfgtool

i.MX6SX Sabreauto board enabled both NAND and QSPI1 drivrers, and by default,
NAND driver built first in kernel compiling, and it would be load first when
Kernel brought up.

Since we could not guarantee all boards mounted NAND chips, we wish the Kernel
could load QSPI driver first, when system mapped QSPI and NAND, the mtd device
index won't change dynamically, otherwise, the mfgtool may write images to the
inappropriate storage devices.

The code change moved the SPI driver at the prior position of NAND driver in
Makefile to solve this issue.

Signed-off-by: Allen Xu <b45815@freescale.com>
(cherry picked from commit 3d2d5724f7a2968b40c2ea0a70c09a3214da1496)