PRODKERNEL: kdump: try to allocate crashkernel memory at the lowest possible address.

Default allocation policy for crashkernel memory is to allocate it at the
highest possible address smaller than CRASH_KERNEL_ADDR_MAX (which is 896M
on x86_64).
This causes failure in kdump kernel because we need memory for pagetable
that covers this big memory range even if we only use 32M.

To decrease kdump kernel memory usage (and actually make kdump kernel work
on 3.10), try to allocate crashkernel at the lowest possible address.
This restores 2.6.34 behavior.

BUG=b/156258896
TEST=presubmit, Manually booted and verified that crashkernel memory was alocated from low addresses.
SOURCE=PRODKERNEL(e5a58ad2d4231a0ee4082907f59b38f5b19339c1)
RELEASE_NOTE=None

Origin-9xx-SHA1: 5cc8448ca103f5a15c2a70581f92ffd811c3cc3f
Origin-11xx-SHA1: e5a58ad2d4231a0ee4082907f59b38f5b19339c1
Upstream-Plan: 185834195
Change-Id: I183f65b0b67b49721e13360b432cca76fbca1680
Signed-off-by: Meena Shanmugam <meenashanmugam@google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/22114
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Oleksandr Tymoshenko <ovt@google.com>
Reviewed-by: Roy Yang <royyang@google.com>