target/riscv: introduce KVM AccelCPUClass

target/riscv: introduce KVM AccelCPUClass

Add a KVM accelerator class like we did with TCG. The difference is
that, at least for now, we won't be using a realize() implementation for
this accelerator.

We'll start by assiging kvm_riscv_cpu_add_kvm_properties(), renamed to
kvm_cpu_instance_init(), as a 'cpu_instance_init' implementation. Change
riscv_cpu_post_init() to invoke accel_cpu_instance_init(), which will go
through the 'cpu_instance_init' impl of the current acceleration (if
available) and execute it. The end result is that the KVM initial setup,
i.e. starting registers and adding its specific properties, will be done
via this hook.

Add a 'tcg_enabled()' condition in riscv_cpu_post_init() to avoid
calling riscv_cpu_add_user_properties() when running KVM. We'll remove
this condition when the TCG accel class get its own 'cpu_instance_init'
implementation.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20230925175709.35696-12-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>