libdtrace: allow D libraries to declare dependencies on kernel modules

libdtrace: allow D libraries to declare dependencies on kernel modules

The "depends_on module" pragma can be used to declare a dependency on a
DTrace module, which for kernel probes corresponds to a KLD. Such
dependencies cannot be checked if the KLD is compiled into the kernel.
Therefore, allow a module dependency to be satisfied if either a kernel
module or a KLD with the specified name is loaded.

Differential Revision:	https://reviews.freebsd.org/D2653
Reviewed by:	gnn, rpaulo
Reported by:	gnn