types.hpp: implement smin, smax, amin, amax

Rewritten the following global utility constants:
`umax` returns max number, restricted to unsigned.
`smax` returns max signed number, restricted to integrals.
`smin` returns min signed number, restricted to signed.
`amin` returns smin or zero, less restricted.
`amax` returns smax or umax, less restricted.

Fix operators == and <=> for synthesized rel-ops.

rpcs3/util/typeindices.hpp

@@ -19,7 +19,7 @@ namespace stx
 	class type_info final : public Info
 	{
 		// Current type id (starts from 0)
-		u32 type = UINT32_MAX;
+		u32 type = umax;
 
 		u32 size = 1;
 		u32 align = 1;