Pica/GPU: Change hardware registers to use physical addresses rather than virtual ones.

This cleans up the mess that address reading/writing had become and makes the code a *lot* more sensible.
This adds a physical<->virtual address converter to mem_map.h. For further accuracy, we will want to properly extend this to support a wider range of address regions. For now, this makes simply homebrew applications work in a good manner though.

src/video_core/pica.h

@@ -45,7 +45,7 @@ struct Regs {
     INSERT_PADDING_WORDS(0x41);
 
     BitField<0, 24, u32> viewport_size_x;
-    INSERT_PADDING_WORDS(1);
+    INSERT_PADDING_WORDS(0x1);
     BitField<0, 24, u32> viewport_size_y;
 
     INSERT_PADDING_WORDS(0x1bc);