TextureCacheBase: Support loading custom mipmaps.

Source/Core/VideoCommon/Src/HiresTextures.h

@@ -25,7 +25,8 @@
 namespace HiresTextures
 {
 void Init(const char *gameCode);
-PC_TexFormat GetHiresTex(const char *fileName, unsigned int *pWidth, unsigned int *pHeight, int texformat, u8 *data);
+bool HiresTexExists(const char *filename);
+PC_TexFormat GetHiresTex(const char *fileName, unsigned int *pWidth, unsigned int *pHeight, unsigned int *required_size, int texformat, unsigned int data_size, u8 *data);
 
 };