uboot-envtools: mvebu: update uci defaults for Turris Omnia

uboot-envtools: mvebu: update uci defaults for Turris Omnia

On the Turris Omnia 2019, u-boot environment is located at 0xF0000, instead
of 0xC0000. The switch happened with u-boot-omnia package version 2019-04-2
(May 10, 2019).

Check the installed u-boot release, and set the default accordingly.

Signed-off-by: Klaus Kudielka <klaus.kudielka@gmail.com>
[bump PKG_RELEASE, use lower case for hex offset]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(cherry picked from commit 04d3b517dc3301e0148a2ce811ffc136568b04bd)