target-lm32: stop VM on illegal or unknown instruction

Instead of translating the instruction to a no-op, pause the VM and display
a message to the user.

As a side effect, this also works for instructions where the operands are
only known at runtime.

Signed-off-by: Michael Walle <michael@walle.cc>
lm32_sys: print test result on stderr

Do not use qemu_log().

Signed-off-by: Michael Walle <michael@walle.cc>
lm32_sys: dump cpu state if test case fails

This will ease debugging the test cases.

Signed-off-by: Michael Walle <michael@walle.cc>
target-lm32: add MMU support

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