target/riscv/kvm/kvm-cpu.c: add missing property getters()

target/riscv/kvm/kvm-cpu.c: add missing property getters()

We got along without property getters in the KVM driver because we never
needed them. But the incoming query-cpu-model-expansion API will use
property getters and setters to retrieve the CPU characteristics.

Add the missing getters for the KVM driver for both MISA and
multi-letter extension properties. We're also adding an special getter
for absent multi-letter properties that KVM doesn't implement that
always return false.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231018195638.211151-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>