Add usart support for L1.

Only tested with basic tx blocking, ie, the same example code as on
F2/F4, but the description of the block is almost identical.

lib/stm32/l1/Makefile

@@ -28,7 +28,7 @@ CFLAGS		= -Os -g -Wall -Wextra -I../../../include -fno-common \
 		  -ffunction-sections -fdata-sections -MD -DSTM32F1
 # ARFLAGS	= rcsv
 ARFLAGS		= rcs
-OBJS		= rcc.o gpio.o desig.o crc.o
+OBJS		= rcc.o gpio.o desig.o crc.o usart.o
 
 VPATH += ../../usb:../:../../cm3
 

lib/stm32/usart.c

@@ -46,6 +46,8 @@ LGPL License Terms @ref lgpl_license
 #	include <libopencm3/stm32/f2/rcc.h>
 #elif defined(STM32F4)
 #	include <libopencm3/stm32/f4/rcc.h>
+#elif defined(STM32L1)
+#	include <libopencm3/stm32/l1/rcc.h>
 #else
 #	error "stm32 family not defined."
 #endif