target/arm: Move '-cpu host' code to cpu64.c

target/arm: Move '-cpu host' code to cpu64.c

Now that KVM has dropped AArch32 host support, the 'host' CPU type is
always AArch64, and we can move it to cpu64.c.  This move will allow
us to share code between it and '-cpu max', which should behave
the same as '-cpu host' when using KVM or HVF.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Alexander Graf <agraf@csgraf.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220204165506.2846058-2-peter.maydell@linaro.org