arm: mach-k3: Add secure device build support

K3 HS devices require signed binaries for boot, use the SECDEV tools
to sign the boot artifacts during build.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Andreas Dannenberg <dannenberg@ti.com>