Support debug and debug-devel sub packages

This commit adds support for building debug and debug-devel sub packages
of the zfs-modules main package. This is to allow building packages
which are built against a debug kernel. By default, only packages are
built against a regular non-debug kernel. This can be toggled by passing
the '--with kernel-debug' parameter to rpmbuild.

Examples:

1. To build packages against only the non-debug kernel $ rpmbuild --rebuild --with kernel --without kernel-debug $SRPM
2. To build packages against only the debug kernel $ rpmbuild --rebuild --without kernel --with kernel-debug $SRPM
3. To build packages against debug and non-debug kernel $ rpmbuild --rebuild --with kernel --with kernel-debug $SRPM

Note: Only the RHEL 5/6, CHAOS 5, and Fedora distributions are supported

for building the debug and debug-devel packages.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>