cpufreq: SPEAr: Instantiate as platform_driver

As multiplatform build is being adopted by more and more
ARM platforms, initcall function should be used very carefully.
For example, when SPEAr cpufreq driver is enabled on a kernel
booted on a non-SPEAr board, we will get following boot time error:

	spear_cpufreq: Invalid cpufreq_tbl

To eliminate this undesired the effect, the patch changes SPEAr
driver to have it instantiated as a platform_driver. Then it will
only run on platforms that create the platform_device "spear-cpufreq".

This patch also creates platform node for SPEAr13xx boards.

Reported-by: Josh Cartwright <joshc@codeaurora.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

arch/arm/mach-spear/spear1310.c

@@ -28,6 +28,7 @@
 static void __init spear1310_dt_init(void)
 {
 	of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
+	platform_device_register_simple("spear-cpufreq", -1, NULL, 0);
 }
 
 static const char * const spear1310_dt_board_compat[] = {

arch/arm/mach-spear/spear1340.c

@@ -143,6 +143,7 @@ static void __init spear1340_dt_init(void)
 {
 	of_platform_populate(NULL, of_default_bus_match_table,
 			spear1340_auxdata_lookup, NULL);
+	platform_device_register_simple("spear-cpufreq", -1, NULL, 0);
 }
 
 static const char * const spear1340_dt_board_compat[] = {