cns3xxx: Enable driver support for onboard m25p80 SPI flash

This device is present on the Gateworks Laguna cns3xxx family.

As the SPI bus master is enabled, also enable driver support for
this typical slave.

[    3.920000] m25p80 spi1.0: found m25p32, expected m25p80
[    3.930000] m25p80 spi1.0: m25p32 (4096 Kbytes)
[    3.930000] Creating 4 MTD partitions on "spi1.0":
[    3.940000] 0x000000000000-0x000000040000 : "uboot"
[    3.940000] 0x000000040000-0x000000080000 : "params"
[    3.950000] 0x000000080000-0x000000200000 : "kernel"
[    3.950000] 0x000000200000-0x000000400000 : "rootfs"

Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>

target/linux/cns3xxx/config-4.4

@@ -185,9 +185,11 @@ CONFIG_MMC_SDHCI_CNS3XXX=y
 CONFIG_MMC_SDHCI_PLTFM=y
 # CONFIG_MMC_TIFM_SD is not set
 CONFIG_MODULES_USE_ELF_REL=y
+CONFIG_MTD_M25P80=y
 # CONFIG_MTD_OF_PARTS is not set
 CONFIG_MTD_PHYSMAP=y
 # CONFIG_MTD_PHYSMAP_OF is not set
+CONFIG_MTD_SPI_NOR=y
 CONFIG_MULTI_IRQ_HANDLER=y
 CONFIG_MUTEX_SPIN_ON_OWNER=y
 CONFIG_NEED_DMA_MAP_STATE=y