[CHERI] Relax an overly strict assertion in cheri_tag_set_many

This is currently called by DCZVA with all zero tag bits and was causing
assertions while running cheribsdtest in Jenkins. The TLBENTRYCAP_FLAG_TRAP
prevents writing non-zero tag bits, but the assertion was triggering for
any value of tags, so relax it to actually model the required condition.

target/cheri-common/cheri_tagmem.c

@@ -679,7 +679,11 @@ void cheri_tag_set_many(CPUArchState *env, uint32_t tags, target_ulong vaddr,
  cheri_debug_assert(!(tagmem_flags & TLBENTRYCAP_FLAG_CLEAR) &&
  "Unimplemented");
 
- cheri_debug_assert(!(tagmem_flags & TLBENTRYCAP_FLAG_TRAP));
+ /*
+ * TLBENTRYCAP_FLAG_TRAP prevents writing non-zero tags, and should have
+ * trapped in probe_cap_write().
+ */
+ assert(tags == 0 || !(tagmem_flags & TLBENTRYCAP_FLAG_TRAP));
 
  cheri_debug_assert(tagmem);