[GPU] Remove magic constants in TEV and texture binding code as much as possible

include/PICA/regs.hpp

@@ -16,7 +16,20 @@ namespace PICA {
 			ShaderOutmap0 = 0x50,
 
 			DepthmapEnable = 0x6D,
+
+			// Texture registers
 			TexUnitCfg = 0x80,
+			Tex0BorderColor = 0x81,
+			Tex1BorderColor = 0x91,
+			Tex2BorderColor = 0x99,
+			TexEnv0Source = 0xC0,
+			TexEnv1Source = 0xC8,
+			TexEnv2Source = 0xD0,
+			TexEnv3Source = 0xD8,
+			TexEnvUpdateBuffer = 0xE0,
+			TexEnv4Source = 0xF0,
+			TexEnv5Source = 0xF8,
+			TexEnvBufferColor = 0xFD,
 
 			// Framebuffer registers
 			ColourOperation = 0x100,