tty: goldfish: Enable 'earlycon' only if built-in

Commit 3840ed9548f7 ("tty: goldfish: Implement support for kernel
'earlycon' parameter") breaks an allmodconfig config on x86:
| LD vmlinux.o
| MODPOST vmlinux.o
|drivers/tty/serial/earlycon.o: In function `parse_options':
|drivers/tty/serial/earlycon.c:97: undefined reference to `uart_parse_earlycon'
|Makefile:1005: recipe for target 'vmlinux' failed

earlycon.c::parse_options() invokes uart_parse_earlycon() from serial_core.c
which is compiled=m because GOLDFISH_TTY itself (and most others) are =m.
To avoid that, I'm adding the _CONSOLE config option which is selected if the
GOLDFISH module itself is =y since it doesn't need the early bits for the =m
case (other drivers do the same dance).
The alternative would be to move uart_parse_earlycon() from
serial_core.c to earlycon.c (we don't have that many users of that
function).

Fixes: 3840ed9548f7 ("tty: goldfish: Implement support for kernel
'earlycon' parameter")
Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Reviewed-by: Miodrag Dinic <[e-mail]>
Acked-by: Miodrag Dinic <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/Kconfig

···
 	depends on GOLDFISH
 	select SERIAL_CORE
 	select SERIAL_CORE_CONSOLE
-	select SERIAL_EARLYCON
 	help
 	  Console and system TTY driver for the Goldfish virtual platform.
+
+config GOLDFISH_TTY_EARLY_CONSOLE
+	bool
+	default y if GOLDFISH_TTY=y
+	select SERIAL_EARLYCON
 
 config DA_TTY
 	bool "DA TTY"

drivers/tty/goldfish.c

···
 	return 0;
 }
 
+#ifdef CONFIG_GOLDFISH_TTY_EARLY_CONSOLE
 static void gf_early_console_putchar(struct uart_port *port, int ch)
 {
 	__raw_writel(ch, port->membase);
···
 }
 
 OF_EARLYCON_DECLARE(early_gf_tty, "google,goldfish-tty", gf_earlycon_setup);
+#endif
 
 static const struct of_device_id goldfish_tty_of_match[] = {
 	{ .compatible = "google,goldfish-tty", },