serial: cpm_uart: Protect udbg definitions by CONFIG_SERIAL_CPM_CONSOLE

If CONFIG_CONSOLE_POLL=y, and CONFIG_SERIAL_CPM=m (hence
CONFIG_SERIAL_CPM_CONSOLE=n):

    drivers/tty/serial/cpm_uart/cpm_uart_core.c:1109:12: warning: ‘udbg_cpm_getc’ defined but not used [-Wunused-function]
     1109 | static int udbg_cpm_getc(void)
	  |            ^~~~~~~~~~~~~
    drivers/tty/serial/cpm_uart/cpm_uart_core.c:1095:13: warning: ‘udbg_cpm_putc’ defined but not used [-Wunused-function]
     1095 | static void udbg_cpm_putc(char c)
	  |             ^~~~~~~~~~~~~

Fix this by making the udbg definitions depend on
CONFIG_SERIAL_CPM_CONSOLE, in addition to CONFIG_CONSOLE_POLL.

Fixes: a6052609 ("tty: serial: cpm_uart: Add udbg support for enabling xmon")
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20211027075326.3270785-1-geert@linux-m68k.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/cpm_uart/cpm_uart_core.c

@@ -1090,6 +1090,7 @@ static void cpm_put_poll_char(struct uart_port *port,
 	cpm_uart_early_write(pinfo, ch, 1, false);
 }
 
+#ifdef CONFIG_SERIAL_CPM_CONSOLE
 static struct uart_port *udbg_port;
 
 static void udbg_cpm_putc(char c)
@@ -1114,6 +1115,7 @@ static int udbg_cpm_getc(void)
 		cpu_relax();
 	return c;
 }
+#endif /* CONFIG_SERIAL_CPM_CONSOLE */
 
 #endif /* CONFIG_CONSOLE_POLL */