Some designs might wish to use an open drain eSPI ALERT#. This change adds an enum that allows setting the eSPI alert mode. BUG=b:187122344, b:186135022 TEST=Boot guybrush using all 3 alert modes Signed-off-by: Raul E Rangel <rrangel@chromium.org> Change-Id: Ia35fc59a699cf9444b53aad5c9bb71aa27ce9251 Reviewed-on: https://review.coreboot.org/c/coreboot/+/52954 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Karthik Ramasubramanian <kramasub@google.com> Reviewed-by: Furquan Shaikh <furquan@google.com>