package_manager: Move OpkgDpkgPM into common module

The OpkgDpkgPM class was introduced to share common functionality
between the Opkg and Debian package manager implementations. However,
for unknown reasons , the refactoring done in
5bc67f55028407de78ac09f97f9a47b165ae8760 duplicated the common class
into the deb and ipk modules. Undo this part of the change by moving the
common base class into a newly created module.

The two variants did not diverge a lot (next to the payload name
generalization, the Debian variant missed
17e2eaed036e1da8e7cb42cb3de51b9523ba54ec) and as such no regressions
should be expected.

Signed-off-by: Philip Lorenz <philip.lorenz@bmw.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>