cpufreq: tegra: create CONFIG_ARM_TEGRA_CPUFREQ

currently Tegra cpufreq driver gets built based on ARCH_TEGRA, which doesn't
depend on nor select CPU_FREQ itself, so:

        select CPU_FREQ_TABLE if CPU_FREQ

... isn't guaranteed to fire.

The correct solution seems to be:

* Add CONFIG_ARM_TEGRA_CPUFREQ to drivers/cpufreq/Kconfig.arm.
* Make that Kconfig option selct CPU_FREQ_TABLE.
* Make that Kconfig option be def_bool ARCH_TEGRA.
* Modify drivers/cpufreq/Makefile to build tegra-cpufreq.c based on that.
* Remove all the cpufreq-related stuff from arch/arm/mach-tegra/Kconfig.

That way, tegra-cpufreq.c can't be built if !CPU_FREQ, and Tegra's
cpufreq works the same way as all the other cpufreq drivers.

This patch does it.

Suggested-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
index 13c3f83..9c873e7 100644
--- a/drivers/cpufreq/Makefile
+++ b/drivers/cpufreq/Makefile
@@ -71,7 +71,7 @@
 obj-$(CONFIG_ARM_SA1100_CPUFREQ)	+= sa1100-cpufreq.o
 obj-$(CONFIG_ARM_SA1110_CPUFREQ)	+= sa1110-cpufreq.o
 obj-$(CONFIG_ARM_SPEAR_CPUFREQ)		+= spear-cpufreq.o
-obj-$(CONFIG_ARCH_TEGRA)		+= tegra-cpufreq.o
+obj-$(CONFIG_ARM_TEGRA_CPUFREQ)		+= tegra-cpufreq.o
 
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 # PowerPC platform drivers