target/arm: Enable FEAT_MEC in -cpu max

target/arm: Enable FEAT_MEC in -cpu max

Advertise FEAT_MEC in AA64MMFR3 ID register for the Arm64 cpu max as a
first step to fully support FEAT_MEC.

The FEAT_MEC is an extension to FEAT_RME that implements multiple
Memory Encryption Contexts (MEC) so the memory in a realm can be
encrypted and accessing it from the wrong encryption context is not
possible. An encryption context allow the selection of a memory
encryption engine.

At this point, no real memory encryption is supported, but software
stacks that rely on FEAT_MEC should work properly.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
Message-id: 20251006001018.219756-4-gustavo.romero@linaro.org
Message-ID: <20250711140828.1714666-7-gustavo.romero@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>