linux-user/aarch64: Enable hwcap for RND, BTI, and MTE

These three features are already enabled by TCG, but are missing
their hwcap bits.  Update HWCAP2 from linux v5.12.

Cc: qemu-stable@nongnu.org (for 6.0.1)
Buglink: https://bugs.launchpad.net/bugs/1926044


Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210427214108.88503-1-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>