package.bbclass: Switch shlibs to pkgdata directory and make package non-machine...

package.bbclass: Switch shlibs to pkgdata directory and make package non-machine specific

Currently, do_package is machine specific since the shlibs data is installed
into each machine specific sysroot. This change moves the shlibs data to the
pkgdata structure, at the expense of having to iterate over a set of shlibs
directories instead of a single one.

It turns out this isn't any particular hardship for the code and as a result,
do_package stops being machine specific leading to optimisations for builds
that use a common PACKAGE_ARCH.

(From OE-Core rev: cc088489d70fb27d460c3dbe35d6ea382123c134)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>