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>

lib/efi/efi_stub.c

@@ -59,7 +59,7 @@ struct __packed desctab_info {
  * considering if we start needing more U-Boot functionality. Note that we
  * could then move get_codeseg32() to arch/x86/cpu/cpu.c.
  */
-void debug_uart_init(void)
+void _debug_uart_init(void)
 {
 }