soc/sifive/fu540: Switch clock to 1GHz in romstage

Invoke clock_init in romstage for SiFive Unleashed.

Change-Id: Ib869762d557e8fdf4c83a53698102df116d80389
Signed-off-by: Philipp Hug <philipp@hug.cx>
Reviewed-on: https://review.coreboot.org/28602
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/sifive/hifive-unleashed/romstage.c

@@ -13,8 +13,13 @@
  * GNU General Public License for more details.
  */
 
+#include <cbmem.h>
 #include <console/console.h>
+#include <console/streams.h>
+#include <console/uart.h>
 #include <program_loading.h>
+#include <soc/clock.h>
+#include <soc/sdram.h>
 
 void main(void)
 {
@@ -22,5 +27,18 @@ void main(void)
 
 	/* TODO: Follow Section 6.3 (FSBL) of the FU540 manual */
 
+	/*
+	 * Flush console before changing clock/UART divisor to prevent garbage
+	 * being printed.
+	 */
+	console_tx_flush();
+
+	clock_init();
+
+	// re-initialize UART
+	#if (IS_ENABLED(CONFIG_CONSOLE_SERIAL))
+		uart_init(CONFIG_UART_FOR_CONSOLE);
+	#endif
+
 	run_ramstage();
 }