disas/riscv: Encapsulate opcode_data into decode

disas/riscv: Encapsulate opcode_data into decode

This patch adds a reference to a struct rv_opcode_data object
into struct rv_decode. This further allows to remove all references
to the global variable opcode_data (which is renamed to rvi_opcode_data).

This patch does not introduce any functional change, but prepares
the code for more struct rv_opcode_data objects in the future.

This patch is based on previous work from Liu Zhiwei:
  https://lists.nongnu.org/archive/html/qemu-devel/2022-08/msg03662.html

Co-developed-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: <20230612111034.3955227-6-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>