ANDROID: gki_defconfig: initialize locals with zeroes

This patch switches compiler-based stack initialization from 0xAA
to zero pattern, resulting in much more efficient code and saner
defaults for uninitialized local variables.

Bug: 154198143
Test: run cuttlefish and observe the following lines in dmesg:
      test_stackinit: all tests passed!
      test_meminit: all 130 tests passed!

Signed-off-by: Alexander Potapenko <glider@google.com>
Change-Id: If9f2047fcbee58b90dbd8ad45707c5b40a654e2d