apm821xx: set DEVICE_TYPE to "nas" for sata subtarget

Since DEVICE_TYPE cannot be set per device, just set DEVICE_TYPE
to "nas" for the entire subtarget, which only contains this single
device.

Note that while this looks like a cosmetic change in combination
with the previous patches, this particular patch actually changes
the packages for the device.

Suggested-by: Christian Lamparter <chunkeey@gmail.com>
Cc: Christian Lamparter <chunkeey@gmail.com>
Cc: Sungbo Eo <mans0n@gorani.run>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/apm821xx/sata/target.mk

@@ -1,4 +1,5 @@
 BOARDNAME := Devices which boot from SATA (NAS)
+DEVICE_TYPE := nas
 FEATURES += ext4 usb ramdisk squashfs rootfs-part boot-part
 DEFAULT_PACKAGES += badblocks block-mount e2fsprogs kmod-hwmon-drivetemp \
 		    kmod-dm kmod-md-mod partx-utils mkf2fs f2fsck