x86: reserve highmem pages via reserve_early

This patch makes early reserved highmem pages become reserved
pages. This can be used for highmem pages allocated by bootloader such
as EFI memory map, linked list of setup_data, etc.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Cc: andi@firstfloor.org
Cc: mingo@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>