target/arm: Treat SCTLR_EL1.M as if it were zero when HCR_EL2.TGE is set

target/arm: Treat SCTLR_EL1.M as if it were zero when HCR_EL2.TGE is set

One of the required effects of setting HCR_EL2.TGE is that when
SCR_EL3.NS is 1 then SCTLR_EL1.M must behave as if it is zero for
all purposes except direct reads. That is, it effectively disables
the MMU for the NS EL0/EL1 translation regime.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180724115950.17316-6-peter.maydell@linaro.org