debug_uart: Adjust the declaration of debug_uart_init()

We want to be able to add other common code to this function. So change the
driver's version to have an underscore before it, just like
_debug_uart_putc(). Define debug_uart_init() to call this version.

Update all drivers to this new method.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index 6275a11..6433844 100644
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -257,7 +257,7 @@
 			(1 << CONFIG_DEBUG_UART_SHIFT), \
 		CONFIG_DEBUG_UART_SHIFT)
 
-void debug_uart_init(void)
+static inline void _debug_uart_init(void)
 {
 	struct NS16550 *com_port = (struct NS16550 *)CONFIG_DEBUG_UART_BASE;
 	int baud_divisor;