target/arm: Disable cryptographic instructions when neon is disabled

target/arm: Disable cryptographic instructions when neon is disabled

As of now, cryptographic instructions ISAR fields are never cleared so
we can end up with a cpu with cryptographic instructions but no
floating-point/neon instructions which is not a possible configuration
according to Arm specifications.

In QEMU, we have 3 kinds of cpus regarding cryptographic instructions:
+ no support
+ cortex-a57/a72: cryptographic extension is optional,
  floating-point/neon is not.
+ cortex-a53: crytographic extension is optional as well as
  floating-point/neon. But cryptographic requires
  floating-point/neon support.

Therefore we can safely clear the ISAR fields when neon is disabled.

Note that other Arm cpus seem to follow this. For example cortex-a55 is
like cortex-a53 and cortex-a76/cortex-a710 are like cortex-a57/a72.

Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220427090117.6954-1-damien.hedde@greensocs.com
[PMM: fixed commit message typos]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>