treewide: move mktplinkfw to tplink-v1-image in image-commands.mk

treewide: move mktplinkfw to tplink-v1-image in image-commands.mk

This move the slightly different target-specific implementations of
mktplinkfw from the targets to include/image-commands.mk and renames
it to tplink-v1-image. Having a common version will increase
consistency between implementation and will complete the
tplink build command already present in the new location.

Due to the slight differences of the original implementations, this
also does some adjustments to the device build commands/variables.

This also moves rootfs_align as this is required as dependency.

Tested on:
- TL-WDR4300 v1 (ath79, factory)
- TL-WDR4900 v1 (mpc85xx, sysupgrade)
- RE210 v1 (ramips, see Tested-by)

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Tested-by: Christoph Krapp <achterin@googlemail.com>