nissa/nereid: increase main stack size
nissa/nereid: increase main stack size

We've observed this reported as full. Increase it to prevent memory
corruption due to stack overflow.

BUG=b:218436977
TEST=`kernel stacks` no longer reports main stack at 100% usage,
     currently using 1328 bytes.
BRANCH=none

Signed-off-by: Peter Marheine <ef0b2c492edde94778d7465bfbaeed52c5be6858@chromium.org>
Change-Id: I20e63b6417724db4cd5a3b13b84c162a6ae13414
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3449989
Reviewed-by: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>

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