watch library: implement UART

watch-library/hardware/hw/driver_init.h

@@ -33,6 +33,7 @@ extern "C" {
 #include <hal_ext_irq.h>
 #include <hal_i2c_m_sync.h>
 #include <hal_spi_m_sync.h>
+#include <hal_usart_sync.h>
 #include <hal_delay.h>
 #include <hal_slcd_sync.h>
 
@@ -40,6 +41,8 @@ extern struct adc_sync_descriptor ADC_0;
 
 extern struct i2c_m_sync_desc I2C_0;
 
+extern struct usart_sync_descriptor USART_0;
+
 extern struct slcd_sync_descriptor SEGMENT_LCD_0;
 
 void I2C_0_CLOCK_init(void);