target/riscv: Add orc.b instruction for Zbb, removing gorc/gorci

target/riscv: Add orc.b instruction for Zbb, removing gorc/gorci

The 1.0.0 version of Zbb does not contain gorc/gorci.  Instead, a
orc.b instruction (equivalent to the orc.b pseudo-instruction built on
gorci from pre-0.93 draft-B) is available, mainly targeting
string-processing workloads.

This commit adds the new orc.b instruction and removed gorc/gorci.

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: 20210911140016.834071-12-philipp.tomsich@vrull.eu
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>