mm: disable kernelcore=mirror when no mirror memory

For system with kernelcore=mirror enabled while no mirrored memory is
reported by efi.  This could lead to kernel OOM during startup since all
memory beside zone DMA are in the movable zone and this prevents the
kernel to use it.

Zone DMA/DMA32 initialization is independent of mirrored memory and their
max pfn is set in zone_sizes_init().  Since kernel can fallback to zone
DMA/DMA32 if there is no memory in zone Normal, these zones are seen as
mirrored memory no mather their memory attributes are.

To solve this problem, disable kernelcore=mirror when there is no real
mirrored memory exists.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ma Wupeng <[email protected]>
Suggested-by: Kefeng Wang <[email protected]>
Suggested-by: Mike Rapoport <[email protected]>
Reviewed-by: Mike Rapoport (IBM) <[email protected]>
Reviewed-by: Kefeng Wang <[email protected]>
Cc: Levi Yun <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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