Set RPM_DEFINE_COMMON options

When the kmod packaging was introduced the ability to pass the
--enable-debug and --enable-dmu-tx options from configure all
the way through to make rpm|deb was accidenally lost. Update
ZFS_AC_RPM to explicitlu set RPM_DEFINE_COMMON with these
rpmbuild defines.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1402