Revert 'x86: Fix system crash when loading with "reservetop" parameter'

After close looking, commit 8126dec3 will break:

 1. some cpu feature  in early stage too, like cpu_has_x2apic
 2. will break built-in-command line
 3. will break other memmap= and mem=
 4. early_dbgp and early_console that will use early_ioremap to access mmio (?)

So revert it.

Reported-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>,
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Cc: Andrew Morton <akpm@linux-foundation.org>,
LKML-Reference: <4AB51DFD.2000904@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>