Enable dtrace support for mips64 and the ERL kernel config

Turn on the required options in the ERL config file, and ensure
that the fbt module is listed as a dependency for mips in
the modules/dtrace/dtraceall/dtraceall.c file.

PR: 220346
Reviewed by: gnn, markj
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D12227