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/serial_efi.c b/drivers/serial/serial_efi.c
index cf57d89..ea25c25 100644
--- a/drivers/serial/serial_efi.c
+++ b/drivers/serial/serial_efi.c
@@ -107,7 +107,7 @@
  * There is nothing to init here since the EFI console is already running by
  * the time we enter U-Boot.
  */
-void debug_uart_init(void)
+static inline void _debug_uart_init(void)
 {
 }