mmt: comment out an assert that makes things not work(TM)

It should be investigated!
mmt/nv: add support for the mmio_read/write IOCTLs

This is partial support. Hackzsam may have a better one IIRC.
Of the top of my head, we understood one flag that was telling the
mmio reg should be changed in the pgraph context of the app who
called the IOCTL.