Video_Software: Implement proper RGBA8 texture loading from tmem.

For RGBA8 textures, AR and GB tiles are stored in separate tmem banks. TextureDecoder did not support that previously.

Source/Core/VideoCommon/Src/TextureDecoder.cpp

@@ -2515,6 +2515,28 @@ void TexDecoder_DecodeTexel(u8 *dst, const u8 *src, int s, int t, int imageWidth
 	}
 }
 
+void TexDecoder_DecodeTexelRGBA8FromTmem(u8 *dst, const u8 *src_ar, const u8* src_gb, int s, int t, int imageWidth)
+{
+	u16 sBlk = s >> 2;
+	u16 tBlk = t >> 2;
+	u16 widthBlks = (imageWidth >> 2) + 1;
+	u32 base_ar = (tBlk * widthBlks + sBlk) << 4;
+	u32 base_gb = (tBlk * widthBlks + sBlk) << 4;
+	u16 blkS = s & 3;
+	u16 blkT =  t & 3;
+	u32 blk_off = (blkT << 2) + blkS;
+
+	u32 offset_ar = (base_ar + blk_off) << 1;
+	u32 offset_gb = (base_gb + blk_off) << 1;
+	const u8* val_addr_ar = src_ar + offset_ar;
+	const u8* val_addr_gb = src_gb + offset_gb;
+
+	dst[3] = val_addr_ar[0]; // A
+	dst[0] = val_addr_ar[1]; // R
+	dst[1] = val_addr_gb[0]; // G
+	dst[2] = val_addr_gb[1]; // B
+}
+
 
 const char* texfmt[] = {
 	// pixel