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/clReadWriteImage/CMakeLists.txt

@@ -8,6 +8,7 @@ set(${MODULE_NAME}_SOURCES
     test_read_2D_array.cpp
     test_loops.cpp
     test_read_3D.cpp
+    ../common.cpp
 )
 
 include(../../CMakeCommon.txt)