cpufreq: arm-big-little: Make driver dependent on CONFIG_BIG_LITTLE

The arm_big_little cpufreq driver is only used by ARM bigLITTLE
platforms and hence must depend on CONFIG_BIG_LITTLE.

This was highlighted by Russell earlier when he reported this issue:

drivers/built-in.o: In function `bL_cpufreq_set_rate':
powercap_sys.c:(.text+0x5ed9a0): undefined reference to `bL_switch_request_cb'
Reported-by: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/Kconfig.arm

@@ -4,7 +4,7 @@
 
 config ARM_BIG_LITTLE_CPUFREQ
 	tristate "Generic ARM big LITTLE CPUfreq driver"
-	depends on ARM && ARM_CPU_TOPOLOGY && HAVE_CLK
+	depends on ARM && BIG_LITTLE && ARM_CPU_TOPOLOGY && HAVE_CLK
 	select PM_OPP
 	help
 	  This enables the Generic CPUfreq driver for ARM big.LITTLE platforms.