add MMU flag to CFG2 register
add MMU flag to CFG2 register

Use the most significant bit because Lattice will likely add new feature at
the lower bits.

Signed-off-by: Michael Walle <17b9e1c64588c7fa6419b4d29dc1f4426279ba01@walle.cc>

litex-hub/pythondata-cpu-lm32,litex-hub/pythondata-cpu-lm32