boards/b-l475e-iot01a: use common rtt configuration

boards/b-l475e-iot01a/Makefile.include

@@ -2,6 +2,9 @@
 export CPU = stm32l4
 export CPU_MODEL = stm32l475vg
 
+# we use shared STM32 configuration snippets
+INCLUDES += -I$(RIOTBOARD)/common/stm32/include
+
 # define the default port depending on the host OS
 PORT_LINUX ?= /dev/ttyACM0
 PORT_DARWIN ?= $(firstword $(sort $(wildcard /dev/tty.usbmodem*)))

boards/b-l475e-iot01a/include/periph_conf.h

@@ -20,6 +20,7 @@
 #define PERIPH_CONF_H
 
 #include "periph_cpu.h"
+#include "cfg_rtt_default.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -255,17 +256,6 @@ static const i2c_conf_t i2c_config[] = {
 #define I2C_NUMOF           (sizeof(i2c_config) / sizeof(i2c_config[0]))
 /** @} */
 
-/**
- * @name    RTT configuration
- *
- * On the STM32Lx platforms, we always utilize the LPTIM1.
- * @{
- */
-#define RTT_NUMOF           (1)
-#define RTT_FREQUENCY       (1024U)             /* 32768 / 2^n */
-#define RTT_MAX_VALUE       (0x0000ffff)        /* 16-bit timer */
-/** @} */
-
 /**
  * @name   RTC configuration
  * @{