ARM: S3C64XX: Fix build error with CONFIG_S3C_DEV_FB disabled

If there is no board selecting CONFIG_S3C_DEV_FB enabled, build will
fail on arch/arm/mach-s3c64xx/pm.c, where s3c_device_fb is referenced.

This patch adds ifdef guard around the code making it compile only
when CONFIG_S3C_DEV_FB is enabled.
Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/mach-s3c64xx/pm.c

@@ -338,8 +338,10 @@ int __init s3c64xx_pm_init(void)
 	for (i = 0; i < ARRAY_SIZE(s3c64xx_pm_domains); i++)
 		pm_genpd_init(&s3c64xx_pm_domains[i]->pd, NULL, false);
 
+#ifdef CONFIG_S3C_DEV_FB
 	if (dev_get_platdata(&s3c_device_fb.dev))
 		pm_genpd_add_device(&s3c64xx_pm_f.pd, &s3c_device_fb.dev);
+#endif
 
 	return 0;
 }