target/riscv/cpu.c: split vendor exts from riscv_cpu_extensions[]

target/riscv/cpu.c: split vendor exts from riscv_cpu_extensions[]

Our goal is to make riscv_cpu_extensions[] hold only ratified,
non-vendor extensions.

Create a new riscv_cpu_vendor_exts[] array for them, changing
riscv_cpu_add_user_properties() and riscv_cpu_add_kvm_properties()
accordingly.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Message-ID: <20230912132423.268494-7-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>