A previous patch provides a pointer to the RISCVCPUConfig data.
Let's use this to add the necessary code for vendor extensions.
This patch does not change the current behaviour, but clearly
defines how vendor extension support can be added to the disassembler.

Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Message-Id: <20230612111034.3955227-7-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>