target/riscv: move riscv_cpu_add_kvm_properties() to kvm.c

target/riscv: move riscv_cpu_add_kvm_properties() to kvm.c

We'll introduce the KVM accelerator class with a 'cpu_instance_init'
implementation that is going to be invoked during the common
riscv_cpu_post_init() (via accel_cpu_instance_init()). This
instance_init will execute KVM exclusive code that TCG doesn't care
about, such as adding KVM specific properties, initing registers using a
KVM scratch CPU and so on.

The core of the forementioned cpu_instance_init impl is the current
riscv_cpu_add_kvm_properties() that is being used by the common code via
riscv_cpu_add_user_properties() in cpu.c. Move it to kvm.c, together
will all the relevant artifacts, exporting and renaming it to
kvm_riscv_cpu_add_kvm_properties() so cpu.c can keep using it for now.

To make this work we'll need to export riscv_cpu_extensions,
riscv_cpu_vendor_exts and riscv_cpu_experimental_exts from cpu.c as
well. The TCG accelerator will also need to access those in the near
future so this export will benefit us in the long run.

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: <20230925175709.35696-9-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>