gpio_set_alternate_function() used 0 to mean "normal GPIO function".
But on chips like STM32L, alternate function 0 is actually a function
on some pins. So change "normal GPIO function" to -1.
Also add support for this on STM32L.
BUG=chrome-os-partner:18343
BRANCH=none
TEST=build and boot link and daisy
Change-Id: I9cdd9ad91a315b616e373a0dc9a50545cf9d20fa
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/47903
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
79c6132a6e