RISC-V: Adding XTheadSync ISA extension

This patch adds support for the XTheadSync ISA extension.
The patch uses the T-Head specific decoder and translation.

The implementation introduces a helper to execute synchronization tasks:
helper_tlb_flush_all() performs a synchronized TLB flush on all CPUs.

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: <20230131202013.2541053-3-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/op_helper.c

@@ -258,6 +258,12 @@ void helper_tlb_flush(CPURISCVState *env)
     }
 }
 
+void helper_tlb_flush_all(CPURISCVState *env)
+{
+    CPUState *cs = env_cpu(env);
+    tlb_flush_all_cpus_synced(cs);
+}
+
 void helper_hyp_tlb_flush(CPURISCVState *env)
 {
     CPUState *cs = env_cpu(env);