grunt: Increase port80 buffer to 256 bytes
grunt: Increase port80 buffer to 256 bytes

Increase length of history buffer for port80 messages from 128 to 256.
This is enough to see all messages when resuming from S3 (which currently
produces 211 messages). Booting from S5 produces 848 messages, but making
the buffer that large seems excessive.

BUG=b:117949636
BRANCH=grunt
TEST=See buffer printed after boot and resume

Change-Id: I18a9e95a0a1a96c6bdab54d9a42d1211cd491e20
Signed-off-by: Edward Hill <db1406b34e091703092b6b136bdfeb2c8125fc0e@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1292362
Reviewed-by: Jonathan Brandmeyer <fec1f53cb6eb4426eb62f1a1e49909eafbea899c@chromium.org>

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