selftests/powerpc: Load Monitor Register Tests

Adds two tests. One is a simple test to ensure that the new registers
LMRR and LMSER are properly maintained. The other actually uses the
existing EBB test infrastructure to test that LMRR and LMSER behave as
documented.

Signed-off-by: Jack Miller <jack@codezen.org>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>