FreeBSD: Kernel module should depend on xdr not krpc after 1300092

Since https://reviews.freebsd.org/D24408 FreeBSD provides XDR functions
in the xdr module instead of krpc.

For FreeBSD 13, the MODULE_DEPEND should be changed to xdr

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #10442
Closes #10443