This makes the range reservation feature available to other
architectures.

-v2: add get_max_mapped, max_pfn_mapped only defined in x86...
     to fix PPC compiling
-v3: according to hpa, add CONFIG_HAVE_EARLY_RES
-v4: fix typo about EARLY_RES in config
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
LKML-Reference: <4B7B5723.4070009@kernel.org>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>