change(uart): Use low power HIRC8 for uart clock

This is in preparation of changing the system clock dynamically. The UART needs a stable clock and AFAIK this clock is specifically designed to work well with the UART. It can stays constant during (light) sleep phases.

lib/sdk/Libraries/Boards/card10/Source/board.c

@@ -65,7 +65,7 @@ const uart_cfg_t uart_cfg = {
     .flow   = UART_FLOW_CTRL_DIS,
     .pol    = UART_FLOW_POL_DIS,
     .baud   = CONSOLE_BAUD,
-    .clksel = UART_CLKSEL_SYSTEM
+    .clksel = UART_CLKSEL_ALTERNATE
 };
 
 const sys_cfg_uart_t uart_sys_cfg = {
@@ -117,6 +117,8 @@ int Console_Init(void)
 {
     int err;
 
+    SYS_ClockSourceEnable(SYS_CLOCK_HIRC8);
+
     if ((err = UART_Init(ConsoleUart, &uart_cfg, &uart_sys_cfg)) != E_NO_ERROR) {
         return err;
     }
@@ -133,6 +135,8 @@ int Console_Shutdown(void)
         return err;
     }
 
+    SYS_ClockSourceDisable(SYS_CLOCK_HIRC8);
+
     return E_NO_ERROR;
 }