stm32: activate stop mode
stm32: activate stop mode

Fully enable the EC power management.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BUG=chrome-os-partner:8866
TEST=on Snow, ensure the EC is never freezing when going out of S5.

Change-Id: I1862c4122ef079c1dd8086f9e7acb4b121532fa7
Reviewed-on: https://gerrit.chromium.org/gerrit/29930
Reviewed-by: David Hendricks <3b0deacc4b5357f519084f1ea34bd42bf5d34545@chromium.org>
Reviewed-by: Rong Chang <3a05493f7adfb36d203f663b3bc2ba30e9d6284f@chromium.org>
Tested-by: Rong Chang <3a05493f7adfb36d203f663b3bc2ba30e9d6284f@chromium.org>
Tested-by: <52924548dcf9c70b394d3b0f0e7309ac05937c9f@google.com>
Commit-Ready: <52924548dcf9c70b394d3b0f0e7309ac05937c9f@google.com>

fourier49/BIZ_EC,alterapraxisptyltd/chromium-ec,mtk09422/chromiumos-platform-ec,eatbyte/chromium-ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,longsleep/ec,akappy7/ChromeOS_EC_LED_Diagnostics,thehobn/ec,mtk09422/chromiumos-platform-ec,md5555/ec,coreboot/chrome-ec,fourier49/BIZ_EC,coreboot/chrome-ec,alterapraxisptyltd/chromium-ec,gelraen/cros-ec,coreboot/chrome-ec,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,longsleep/ec,fourier49/BIZ_EC,fourier49/BZ_DEV_EC,md5555/ec,gelraen/cros-ec,gelraen/cros-ec,akappy7/ChromeOS_EC_LED_Diagnostics,longsleep/ec,coreboot/chrome-ec,eatbyte/chromium-ec,eatbyte/chromium-ec,gelraen/cros-ec,thehobn/ec,longsleep/ec,thehobn/ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,alterapraxisptyltd/chromium-ec,eatbyte/chromium-ec,mtk09422/chromiumos-platform-ec,md5555/ec,mtk09422/chromiumos-platform-ec,fourier49/BIZ_EC,thehobn/ec,alterapraxisptyltd/chromium-ec,fourier49/BZ_DEV_EC