SCP: Reduce compiler warnings on LP64 platforms

(Note: Reducing compiler warnings across all, but primarily LP64
platforms, is a long term objective.)

Reduce compiler warnings on LP64 platforms (macOS, Windows) and 32-bit
builds (Win32). Prefer 'size_t' for pointer arithmetic, array indexing
and extents; 'int' hasn't been used for these purposes for many years
and across many ANSI standards. N.B. that conversions from int or int32
to size_t cause the compiler to zero-extend the value, which is
inefficient.

Refactor printf() format modifiers into sim_printf_fmts.h. Add the
SIZE_T_FMT modifier for better portability, especially on LP64 platforms
where size_t is unsigned long and sizeof(size_t) > sizeof(int).

3B2: Fix known size_t printf() format.

3B2/3b2_dmac.c

@@ -185,7 +185,7 @@ uint32 dmac_read(uint32 pa, size_t size)
             break;
         default:
             sim_debug(READ_MSG, &dmac_dev,
-                      "DMAC READ %lu B @ %08x\n",
+                      "DMAC READ %" SIZE_T_FMT "u B @ %08x\n",
                       size, pa);
             data = 0;
         }
@@ -193,7 +193,7 @@ uint32 dmac_read(uint32 pa, size_t size)
         return data;
     default:
         sim_debug(READ_MSG, &dmac_dev,
-                  "[BASE: %08x] DMAC READ %lu B @ %08x\n",
+                  "[BASE: %08x] DMAC READ %" SIZE_T_FMT "u B @ %08x\n",
                   base, size, pa);
         return 0;
     }