x86/gart: Fix kmemleak warning

x86/gart: Fix kmemleak warning

aperture_64.c now is using memblock, the previous
kmemleak_ignore() for alloc_bootmem() should be removed then.

Otherwise, with kmemleak enabled, kernel will throw warnings
like:

[    0.000000] kmemleak: Trying to color unknown object at 0xffff8800c4000000 as Black
[    0.000000] Pid: 0, comm: swapper/0 Not tainted 3.5.0-rc1-next-20120605+ #130
[    0.000000] Call Trace:
[    0.000000]  [<ffffffff811b27e6>] paint_ptr+0x66/0xc0
[    0.000000]  [<ffffffff816b90fb>] kmemleak_ignore+0x2b/0x60
[    0.000000]  [<ffffffff81ef7bc0>] kmemleak_init+0x217/0x2c1
[    0.000000]  [<ffffffff81ed2b97>] start_kernel+0x32d/0x3eb
[    0.000000]  [<ffffffff81ed25e4>] ? repair_env_string+0x5a/0x5a
[    0.000000]  [<ffffffff81ed2356>] x86_64_start_reservations+0x131/0x135
[    0.000000]  [<ffffffff81ed2120>] ? early_idt_handlers+0x120/0x120
[    0.000000]  [<ffffffff81ed245c>] x86_64_start_kernel+0x102/0x111
[    0.000000] kmemleak: Early log backtrace:
[    0.000000]    [<ffffffff816b911b>] kmemleak_ignore+0x4b/0x60
[    0.000000]    [<ffffffff81ee6a38>] gart_iommu_hole_init+0x3e7/0x547
[    0.000000]    [<ffffffff81edb20b>] pci_iommu_alloc+0x44/0x6f
[    0.000000]    [<ffffffff81ee81ad>] mem_init+0x19/0xec
[    0.000000]    [<ffffffff81ed2a54>] start_kernel+0x1ea/0x3eb
[    0.000000]    [<ffffffff81ed2356>] x86_64_start_reservations+0x131/0x135
[    0.000000]    [<ffffffff81ed245c>] x86_64_start_kernel+0x102/0x111
[    0.000000]    [<ffffffffffffffff>] 0xffffffffffffffff

Signed-off-by: Xiaotian Feng <dannyfeng@tencent.com>
Cc: Xiaotian Feng <xtfeng@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/1338922831-2847-1-git-send-email-xtfeng@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>