target/ppc: Remove env->immu_idx and env->dmmu_idx

target/ppc: Remove env->immu_idx and env->dmmu_idx

We weren't recording MSR_GS in hflags, which means that BookE
memory accesses were essentially random vs Guest State.

Instead of adding this bit directly, record the completed mmu
indexes instead.  This makes it obvious that we are recording
exactly the information that we need.

This also means that we can stop directly recording MSR_IR.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210323184340.619757-9-richard.henderson@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>