gsmi: Add coreboot to list of matching BIOS vendors

gsmi: Add coreboot to list of matching BIOS vendors

In order to use this coreboot needs board support for:
CONFIG_ELOG=y
CONFIG_ELOG_GSMI=y

And the kernel driver needs enabled:
CONFIG_GOOGLE_GSMI=y

BUG=chrome-os-partner:9195
TEST=manual

Verify that clean shutdown event is added to the log:

> mosys eventlog list | grep 'Clean Shutdown'
11 | 2012-06-25 09:49:24 | Kernl Event | Clean Shutdown

Change-Id: I01d5aae415207538bf46166c04a874685213386f
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/26029
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>