Rendertarget attachments, texture and image changes (#358)

* Add multiple color outputs for fragment shaders

* Add registers and gal enums

* Use textures for framebuffers and split color and zeta framebuffers

* Abstract texture and framebuffer targets as an image

* Share images between framebuffers and textures

* Unstub formats

* Add some formats

* Disable multiple attachments

* Cache framebuffer attachments

* Handle format types

* Add some rendertarget formats

* Code cleanup

* Fixup half float types

* Address feedback

* Disable multiple attachments in shaders

* Add A4B4G4R4 image format

* Add reversed section for image enums

Ryujinx.Graphics/Gal/GalZetaFormat.cs

@@ -0,0 +1,16 @@
+namespace Ryujinx.Graphics.Gal
+{
+    public enum GalZetaFormat
+    {
+        Z32Float          = 0x0a,
+        Z16Unorm          = 0x13,
+        S8Z24Unorm        = 0x14,
+        Z24X8Unorm        = 0x15,
+        Z24S8Unorm        = 0x16,
+        Z24C8Unorm        = 0x18,
+        Z32S8X24Float     = 0x19,
+        Z24X8S8C8X16Unorm = 0x1d,
+        Z32X8C8X16Float   = 0x1e,
+        Z32S8C8X16Float   = 0x1f
+    }
+}