ipq807x: image: fix eMMC flashing/recovery from within initramfs

ipq807x: image: fix eMMC flashing/recovery from within initramfs

Having initramfs image built with same config as on buildbots:

 CONFIG_TARGET_MULTI_PROFILE=y
 CONFIG_TARGET_ALL_PROFILES=y
 CONFIG_TARGET_PER_DEVICE_ROOTFS=y

Its currently impossible to flash/recover the device using that image as
losetup is missing:

 root@OpenWrt:/# sysupgrade -v /tmp/openwrt-ipq807x-generic-prpl_haze-squashfs-sysupgrade.bin
 ...
 /lib/upgrade/do_stage2: line 38: losetup: not found
 Failed to detach all loop devices. Skip this try.

So lets fix it by including the needed utils for sysupgrade in
DEFAULT_PACKAGES set.

Signed-off-by: Petr Štetiar <ynezz@true.cz>