uart: logging: Add configurable log level to UART drivers

This change adds compile-time selection of log level for
the UART drivers.

Signed-off-by: Pete Dietl <petedietl@gmail.com>
diff --git a/drivers/serial/uart_stm32.c b/drivers/serial/uart_stm32.c
index 7e3aa2f..297e6e4 100644
--- a/drivers/serial/uart_stm32.c
+++ b/drivers/serial/uart_stm32.c
@@ -36,7 +36,7 @@
 #include <stm32_ll_lpuart.h>
 
 #include <logging/log.h>
-LOG_MODULE_REGISTER(uart_stm32);
+LOG_MODULE_REGISTER(uart_stm32, CONFIG_UART_LOG_LEVEL);
 
 #define HAS_LPUART_1 (DT_NODE_HAS_COMPAT_STATUS(DT_NODELABEL(lpuart1), \
 					 st_stm32_lpuart, okay))