DynASM/ARM64: Support ldp/stp of q registers.

Thanks to Peter Cawley. LuaJIT#1096

dynasm/dasm_arm64.lua

@@ -549,7 +549,7 @@ end
 local function parse_load_pair(params, nparams, n, op)
   if params[n+2] then werror("too many operands") end
   local pn, p2 = params[n], params[n+1]
-  local scale = shr(op, 30) == 0 and 2 or 3
+  local scale = 2 + shr(op, 31 - band(shr(op, 26), 1))
   local p1, wb = match(pn, "^%[%s*(.-)%s*%](!?)$")
   if not p1 then
     if not p2 then
@@ -806,8 +806,8 @@ map_op = {
   ["ldrsw_*"] = "98000000DxB|b8800000DxL",
   -- NOTE: ldur etc. are handled by ldr et al.
 
-  ["stp_*"]   = "28000000DAwP|a8000000DAxP|2c000000DAsP|6c000000DAdP",
-  ["ldp_*"]   = "28400000DAwP|a8400000DAxP|2c400000DAsP|6c400000DAdP",
+  ["stp_*"]   = "28000000DAwP|a8000000DAxP|2c000000DAsP|6c000000DAdP|ac000000DAqP",
+  ["ldp_*"]   = "28400000DAwP|a8400000DAxP|2c400000DAsP|6c400000DAdP|ac400000DAqP",
   ["ldpsw_*"] = "68400000DAxP",
 
   -- Branches.
@@ -942,7 +942,7 @@ local function parse_template(params, template, nparams, pos)
 	werror("bad register type")
       end
       parse_reg_type = false
-    elseif p == "x" or p == "w" or p == "d" or p == "s" then
+    elseif p == "x" or p == "w" or p == "d" or p == "s" or p == "q" then
       if parse_reg_type ~= p then
 	werror("register size mismatch")
       end