mpi: Add .note.gnu.property section for Intel CET

* mpi/config.links: Include <cet.h> in <asm-syntax.h>.

When Intel CET is enabled, include <cet.h> in <asm-syntax.h> for
assembly codes to mark Intel CET support.

• Signed-off-by: H.J. Lu <hjl.tools@gmail.com>