RISC-V: Add support for Ztso

RISC-V: Add support for Ztso

The Ztso extension is already ratified, this adds it as a CPU property
and adds various fences throughout the port in order to allow TSO
targets to function on weaker hosts.  We need no fences for AMOs as
they're already SC, the places we need barriers are described.
These fences are placed in the RISC-V backend rather than TCG as is
planned for x86-on-arm64 because RISC-V allows heterogeneous (and
likely soon dynamic) hart memory models.

Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Message-ID: <20240207122256.902627-2-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>