backports: define C code backport version info using CPTCFG_

backports: define C code backport version info using CPTCFG_

In order to help unify the naming scheme for shared
backports versioning information rely on the CPTCFG_
prefix, when integration support gets added that will
translate to the respective CONFIG_BACKPORT_ prefix.
Kconfig opt env entries don't get propagated out, so
we need to define these ourselves. This leaves all
other names in place for packaging and just focuses
on sharing on the C / header code.

Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>