stm32mon: add back flashing progression
stm32mon: add back flashing progression

As we no longer have the low-tech dots to show the progression of the
on-going flashing, display a completion percentage to give the user a
hint of the ETA.

Signed-off-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

BRANCH=none
BUG=none
TEST=./util/flash_ec --board=spring
and see accurate progression percentage reported.

Change-Id: I75ccbe3433acd6c94d03a08bf462ea4516e4ce02
Reviewed-on: https://gerrit.chromium.org/gerrit/42733
Commit-Queue: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Tested-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Reviewed-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>

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