stm32l: fix new line output on the UART
stm32l: fix new line output on the UART

On the STM32L UART without a FIFO, the Transmit Register might need
some time before pushing its content to the shift register.

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

BUG=None
TEST=on ADV board, verify we are no longer missing most of the carriage
return on console.

Change-Id: Ic638dc452d6e30a5f127710fc964143d477fa1d6

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