RPM: Add missing BuildRequires for PAM component

RPM: Add missing BuildRequires for PAM component

When the optional PAM binaries are included in a build, ./configure will
look for security/pam_modules.h and - if it doesn't find it - recommend
the user install `libpam0g-dev`.  On Red Hat systems, `pam-devel` is the
package that supplies this requirement; `libpam0g-dev` does not exist.

By encoding this requirement in the spec file, we give packagers more
appropriate (and timely) recommendations for completing the build.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chris Lindee <chris.lindee+github@gmail.com>
Closes #13001