MIPS: ath25: Avoid undefined early_serial_setup() without SERIAL_8250_CONSOLE

Currently MIPS allnoconfig with CONFIG_ATH25=y fails to link due to
missing support for early_serial_setup():

LD vmlinux
arch/mips/ath25/devices.o: In function ath25_serial_setup':
devices.c:(.init.text+0x68): undefined reference to 'early_serial_setup'

Rather than adding dependencies to the platform to force inclusion of
SERIAL_8250_CONSOLE together with it's dependencies like TTY, HAS_IOMEM,
etc, just make ath25_serial_setup() a no-op when the dependency is not
selected in the kernel config.

Signed-off-by: Matt Redfearn <[e-mail]>
Cc: James Hogan <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Philippe Ombredanne <[e-mail]>
Cc: Kate Stewart <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/17700/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/ath25/devices.c

···
 
 void __init ath25_serial_setup(u32 mapbase, int irq, unsigned int uartclk)
 {
+#ifdef CONFIG_SERIAL_8250_CONSOLE
 	struct uart_port s;
 
 	memset(&s, 0, sizeof(s));
···
 	s.uartclk = uartclk;
 
 	early_serial_setup(&s);
+#endif /* CONFIG_SERIAL_8250_CONSOLE */
 }
 
 int __init ath25_add_wmac(int nr, u32 base, int irq)