packages: Improve handling of -lib packages

For some packages (OpenSSL, Kerberos) we want to ship runtime libraries
in a separate package, e.g. openssl and openssl-lib. Currently this is
done using PACKAGE=openssl-lib, but that creates packages with strange
names like openssl-lib-lib32.

Instead, add a new LIB_PACKAGE option to bsd.lib.mk that causes runtime
libraries to be placed in a new -lib subpackage. This significantly
improves the set of packages we create; for example, OpenSSL goes from:

FreeBSD-openssl
FreeBSD-openssl-dbg
FreeBSD-openssl-lib
FreeBSD-openssl-lib-dbg
FreeBSD-openssl-lib-dbg-lib32
FreeBSD-openssl-lib-dev
FreeBSD-openssl-lib-dev-lib32
FreeBSD-openssl-lib-lib32
FreeBSD-openssl-lib-man
FreeBSD-openssl-man

to:

FreeBSD-openssl
FreeBSD-openssl-dbg
FreeBSD-openssl-dbg-lib32
FreeBSD-openssl-dev
FreeBSD-openssl-dev-lib32
FreeBSD-openssl-lib
FreeBSD-openssl-lib32
FreeBSD-openssl-man

While here, move /usr/bin/krb5-config and /usr/bin/compile_et into
the kerberos-dev package.

Reviewed by: des
Differential Revision: https://reviews.freebsd.org/D51925