ppc: Fix macio ESCC legacy mapping

The current mapping, while correct for the base ports (which is all the
driver uses these days), is wrong for the extended registers.

I suspect the bugs come from incorrect tables in the CHRP IO Ref document,
I have verified the new values here match Apple's MacTech.pdf.

Note: Nothing that I know of actually uses these registers so it's not a
huge deal, but this patch has the added advantage of adding comments to
document what the registers are.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/misc/macio/macio.c

@@ -89,22 +89,16 @@ static void macio_escc_legacy_setup(MacIOState *macio_state)
     MemoryRegion *bar = &macio_state->bar;
     int i;
     static const int maps[] = {
-        0x00, 0x00,
-        0x02, 0x20,
-        0x04, 0x10,
-        0x06, 0x30,
-        0x08, 0x40,
-        0x0A, 0x50,
-        0x60, 0x60,
-        0x70, 0x70,
-        0x80, 0x70,
-        0x90, 0x80,
-        0xA0, 0x90,
-        0xB0, 0xA0,
-        0xC0, 0xB0,
-        0xD0, 0xC0,
-        0xE0, 0xD0,
-        0xF0, 0xE0,
+        0x00, 0x00, /* Command B */
+        0x02, 0x20, /* Command A */
+        0x04, 0x10, /* Data B */
+        0x06, 0x30, /* Data A */
+        0x08, 0x40, /* Enhancement B */
+        0x0A, 0x50, /* Enhancement A */
+        0x80, 0x80, /* Recovery count */
+        0x90, 0x90, /* Start A */
+        0xa0, 0xa0, /* Start B */
+        0xb0, 0xb0, /* Detect AB */
     };
 
     memory_region_init(escc_legacy, OBJECT(macio_state), "escc-legacy", 256);