kernel: Move CodeSet structure to its own source files

Given this is utilized by the loaders, this allows avoiding inclusion of
the kernel process definitions where avoidable.

This also keeps the loading format for all executable data separate from
the kernel objects.

src/core/loader/elf.cpp

@@ -9,6 +9,7 @@
 #include "common/common_types.h"
 #include "common/file_util.h"
 #include "common/logging/log.h"
+#include "core/hle/kernel/code_set.h"
 #include "core/hle/kernel/process.h"
 #include "core/hle/kernel/vm_manager.h"
 #include "core/loader/elf.h"