rose: enable stm32f4 EXTI IRQs
rose: enable stm32f4 EXTI IRQs

This change copied gpio_init() from stm32f373 driver.

BUG=chromium:688979
TEST=load on dev board and check button interrupt
BRANCH=none

Change-Id: I9dc12ffc02899211b6d07a640682899654c2bbed
Signed-off-by: Rong Chang <3a05493f7adfb36d203f663b3bc2ba30e9d6284f@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/438909
Commit-Ready: Wei-Ning Huang <197c169951aeef0485c6aeb1572203d47803b127@chromium.org>
Tested-by: Wei-Ning Huang <197c169951aeef0485c6aeb1572203d47803b127@chromium.org>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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