ARM: OMAP2+: Fix build error for realtime counter init if not enabled

Otherwise we can get an error with some configs:

arch/arm/mach-omap2/timer.c:73: undefined reference to `omap_smc1'
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/timer.c

@@ -66,12 +66,15 @@
 
 static struct omap_dm_timer clkev;
 static struct clock_event_device clockevent_gpt;
+
+#ifdef CONFIG_SOC_HAS_REALTIME_COUNTER
 static unsigned long arch_timer_freq;
 
 void set_cntfreq(void)
 {
 	omap_smc1(OMAP5_DRA7_MON_SET_CNTFRQ_INDEX, arch_timer_freq);
 }
+#endif
 
 static irqreturn_t omap2_gp_timer_interrupt(int irq, void *dev_id)
 {