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/translate.c

@@ -132,7 +132,7 @@ static bool always_true_p(DisasContext *ctx  __attribute__((__unused__)))
 
 static bool has_xthead_p(DisasContext *ctx  __attribute__((__unused__)))
 {
-    return ctx->cfg_ptr->ext_xtheadcmo;
+    return ctx->cfg_ptr->ext_xtheadcmo || ctx->cfg_ptr->ext_xtheadsync;
 }
 
 #define MATERIALISE_EXT_PREDICATE(ext)  \