QNICE V1.7: Get rid of duplicate code in qnice_mmio.vhd

[sy2002]

As soon as QNICE V1.7 is released, we can get rid of qnice_mmio.vhd because V1.7's MMIO controller already lets us switch off PORE using generics.

So we will be able to delete the local copy of qnice_mmio.vhd and just change the usage (switch off PORE) in MEGA65/vhdl/qnice.vhd: mmio_std : entity work.mmio_mux