g: increase usb console TX buffer size to 4K
g: increase usb console TX buffer size to 4K

Increasing the USB console TX buffer size allows to see pretty much
all early startup messages generated before USB console is
initialized.

There is still plenty of room left in SRAM, 23K on cr50, much more on
all other g based boards.

BRANCH=none
BUG=none
TEST=observed better USB console output on cr50 restarts.

Change-Id: I82f37ee7f3aecd8b7e95f3d421789c11375b2fd4
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/364811
Reviewed-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Reviewed-by: Nadim Taha <b42c84a30622c1b59fd137ddd0faa205f9b90636@chromium.org>

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