According to the explaination for pref_address
in Documentation/x86/boot.txt, a relocating bootloader
should attempt to load kernel at pref_address if possible.
But due to a non-relocatable kernel will unconditionally
move itself and to run at perf address, no need to copy
kernel to perf_address by bootloader.
Signed-off-by: Zheng, Gen <gen.zheng@intel.com>