x86: Make sure wakeup trampoline code is below 1MB

Instead of using bootmem, try find_e820_area()/reserve_early(),
and call acpi_reserve_memory() early, to allocate the wakeup
trampoline code area below 1M.

This is more reliable, and it also removes a dependency on
bootmem.

-v2: change function name to acpi_reserve_wakeup_memory(),
     as suggested by Rafael.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: pm list <linux-pm@lists.linux-foundation.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <4AFA210B.3020207@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>