x86/apic: Avoid wrong warning when parsing 'apic=' in X86-32 case

There are two consumers of apic=:
  apic_set_verbosity() for setting the APIC debug level;
  parse_apic() for registering APIC driver by hand.

X86-32 supports both of them, but sometimes, kernel issues a weird warning.
eg: when kernel was booted up with 'apic=bigsmp' in command line,
early_param would warn like that:

...
[    0.000000] APIC Verbosity level bigsmp not recognised use apic=verbose or apic=debug
[    0.000000] Malformed early option 'apic'
...

Wrap the warning code in CONFIG_X86_64 case to avoid this.
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: peterz@infradead.org
Cc: rdunlap@infradead.org
Cc: corbet@lwn.net
Link: https://lkml.kernel.org/r/20171204040313.24824-1-douly.fnst@cn.fujitsu.com

arch/x86/kernel/apic/apic.c

@@ -2626,11 +2626,13 @@ static int __init apic_set_verbosity(char *arg)
 		apic_verbosity = APIC_DEBUG;
 	else if (strcmp("verbose", arg) == 0)
 		apic_verbosity = APIC_VERBOSE;
+#ifdef CONFIG_X86_64
 	else {
 		pr_warning("APIC Verbosity level %s not recognised"
 			" use apic=verbose or apic=debug\n", arg);
 		return -EINVAL;
 	}
+#endif
 
 	return 0;
 }