s6e63m0: add mcde channel entry (by cocafe)

This entry allows us to write the params of mcde/chnl0(s6e63m0 uses).

        Write params first, for example:
        echo pclk=50000 > mcde_chnl

        Update channel config:
        echo update > mcde_chnl

Screen will stop playing until we send an event to active it again(namely, touching the screen).