target/riscv: add a MAINTAINERS entry for XVentanaCondOps

target/riscv: add a MAINTAINERS entry for XVentanaCondOps

The XVentanaCondOps extension is supported by VRULL on behalf of the
Ventana Micro.  Add myself as a point-of-contact.

Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220202005249.3566542-8-philipp.tomsich@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>