ANDROID: GKI: arch: add stub symbols for boot_reason and cold_boot

These symbols are needed by some vendor drivers. So add stubs symbols to
please those drivers.

Bug: 153902877
Test: compile
Signed-off-by: Rick Adams <rgadams@codeaurora.org>
Signed-off-by: David Keitel <dkeitel@codeaurora.org>
Signed-off-by: David Collins <collinsd@codeaurora.org>
[willmcvicker: Squashed the following commits but only took ABI diffs:
  f699c92b61 msm: 8x55: put reason for boot in procfs from SMEM
  ee67650037 sysctl: add cold_boot sysctl entry
  de98b0ac25 sysctl: add boot_reason and cold_boot sysctl entries for arm64]
Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: I1c3eb7bcf9fb2ccae870a3fb4b9e31138609cf46