icd:Increase WHOLE_SIZE mapped memory

Bump hard-coded mapped memory allocation size for WHOLE_SIZE from 4k to
64k. One validation test (InvalidMemoryMapping) was mapping 64k of
memory that was leading to segF as the 4k buffer was overwritten when
shadowed.
diff --git a/scripts/mock_icd_generator.py b/scripts/mock_icd_generator.py
index 7a10c5d..3366aa1 100644
--- a/scripts/mock_icd_generator.py
+++ b/scripts/mock_icd_generator.py
@@ -648,9 +648,9 @@
 ''',
 'vkMapMemory': '''
     unique_lock_t lock(global_lock);
-    // TODO: Just hard-coding 4k whole size for now
+    // TODO: Just hard-coding 64k whole size for now
     if (VK_WHOLE_SIZE == size)
-        size = 4096;
+        size = 0x10000;
     void* map_addr = malloc((size_t)size);
     mapped_memory_map[memory].push_back(map_addr);
     *ppData = map_addr;