Merge pull request #11417 from Turim:imgcodecs_cmake_decoders_customize_formats

* imgcodecs cmake: the option to customize supported formats list (WITH_IMGCODEC_HDR, WITH_IMGCODEC_SUNRASTER, WITH_IMGCODEC_PXM)

* imgcodecs: fixes

- fixed CMake scripts (=OFF doesn't really work)
- restore dropped GDCM block
- added _IMGCODEC_ prefix
- fixed tests
- include PAM format under WITH_IMGCODEC_PXM option

modules/imgcodecs/test/test_read_write.cpp

@@ -112,8 +112,12 @@ const string exts[] = {
     "exr",
 #endif
     "bmp",
+#ifdef HAVE_IMGCODEC_PXM
     "ppm",
-    "ras"
+#endif
+#ifdef HAVE_IMGCODEC_SUNRASTER
+    "ras",
+#endif
 };
 
 INSTANTIATE_TEST_CASE_P(imgcodecs, Imgcodecs_Image, testing::ValuesIn(exts));