grunt: Add CONFIG_VSTORE
grunt: Add CONFIG_VSTORE

Add a slot of secure temporary storage to support suspend/resume.

Signed-off-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>

BUG=b:72188897
TEST=On grunt w/ S3-enabled coreboot:
  powerd_dbus_suspend --wakeup_timeout=10
 => Device resumes throught coreboot to kernel
BRANCH=none

Change-Id: I37410a3e66fc6eee32e559069a33e904880cddc9
Reviewed-on: https://chromium-review.googlesource.com/875418
Commit-Ready: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>
Tested-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>
Reviewed-by: Edward Hill <db1406b34e091703092b6b136bdfeb2c8125fc0e@chromium.org>
Reviewed-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>
Reviewed-by: Justin TerAvest <f2d83486a72e2fb2fbfb163be787ddf5d8d3393e@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec