ipq807x: prpl haze & qnap 301w: use the standard eMMC sysupgrade code

ipq807x: prpl haze & qnap 301w: use the standard eMMC sysupgrade code

Note that the old ad-hoc method did not explicitly align backup data
to 64 KiB boundaries.

Also note that the qnap 301w has a 'rootfs_data' partition in the eMMC
that is being ignored by fstools during boot, presumably due to a bug.
This is why the partition is also ignored in the sysupgrade code and
there is no definition of CI_DATAPART="rootfs_data".

Signed-off-by: Rodrigo Balerdi <lanchon@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/16505
Signed-off-by: Robert Marko <robimarko@gmail.com>