Remove duplicate format functions (#738)

This moves the filter_formats and get_format_list functions to a common
file. These functions were roughly the same, with an optional filtering
in some tests for testing mipmaps.

Signed-off-by: Radek Szymanski <radek.szymanski@arm.com>

test_conformance/images/clFillImage/CMakeLists.txt

@@ -11,6 +11,7 @@ set(${MODULE_NAME}_SOURCES
     test_loops.cpp
     test_fill_3D.cpp
 #    test_fill_2D_3D.cpp
+    ../common.cpp
 )