dm: serial: Move baud rate calculation to ns16550.c

Move the function that calculates the baud rate divisor into ns16550.c so
it can be used by that file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index 079f67d..3f5f4ef 100644
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -4,7 +4,7 @@
  * modified to use CONFIG_SYS_ISA_MEM and new defines
  */
 
-#include <config.h>
+#include <common.h>
 #include <ns16550.h>
 #include <watchdog.h>
 #include <linux/types.h>
@@ -45,6 +45,22 @@
 #define CONFIG_SYS_NS16550_IER  0x00
 #endif /* CONFIG_SYS_NS16550_IER */
 
+int ns16550_calc_divisor(NS16550_t port, int clock, int baudrate)
+{
+	const unsigned int mode_x_div = 16;
+
+#ifdef CONFIG_OMAP1510
+	/* If can't cleanly clock 115200 set div to 1 */
+	if ((clock == 12000000) && (baudrate == 115200)) {
+		port->osc_12m_sel = OSC_12M_SEL;  /* enable 6.5 * divisor */
+		return 1;			/* return 1 for base divisor */
+	}
+	port->osc_12m_sel = 0;			/* clear if previsouly set */
+#endif
+
+	return DIV_ROUND_CLOSEST(clock, mode_x_div * baudrate);
+}
+
 void NS16550_init(NS16550_t com_port, int baud_divisor)
 {
 #if (defined(CONFIG_SPL_BUILD) && defined(CONFIG_OMAP34XX))