x86: relax RAM check in ioremap()

Kevin Winchester reported the loss of direct rendering, due to:

[    0.588184] agpgart: Detected AGP bridge 0
[    0.588184] agpgart: unable to get memory for graphics translation table.
[    0.588184] agpgart: agp_backend_initialize() failed.
[    0.588207] agpgart-amd64: probe of 0000:00:00.0 failed with error -12

and bisected it down to:

  commit 266b9f87
  Author: Thomas Gleixner <tglx@linutronix.de>
  Date:   Wed Jan 30 13:34:06 2008 +0100

      x86: fix ioremap RAM check

this check was too strict and caused an ioremap() failure.

the problem is due to the somewhat unclean way of how the GART code
reserves a memory range for its aperture, and how it utilizes it
later on.

Allow RAM pages to be ioremap()-ed too, as long as they are reserved.

Bisected-by: Kevin Winchester <kjwinchester@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Tested-by: Kevin Winchester <kjwinchester@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>