package.bbclass: export subpackage individual version, if different from main

package.bbclass: export subpackage individual version, if different from main

Fixes the wrong versioned runtime dependency for shlib subpackages with
own versions. Consider this:

PACKAGES = "libfoo libbar"
PV_libfoo = "1"
PV_libbar = "2"
PV = "3"

That will generate libfoo_1 and libbar_2 packages, but version 3 will be
exported in shlibs database, leading to the following versioned runtime
dependencies:

RDEPENDS: libfoo (>=3) libbar (>=3)

This fixes the problem.

Signed-off-by: Denys Dmytriyenko <denis@denix.org>
Acked-by: Koen Kooi <koen@openembedded.org>