ARM: tegra: Guard powergate code with a Kconfig symbol

Powergate code is not relevant on all Tegra SoC generations, so guard it
with a Kconfig symbol that can be selected by the generations that need
it.

This is in preparation for unifying Tegra186 code with the code used on
older generations.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/arch/arm/mach-tegra/Makefile b/arch/arm/mach-tegra/Makefile
index 395e019..517be21 100644
--- a/arch/arm/mach-tegra/Makefile
+++ b/arch/arm/mach-tegra/Makefile
@@ -18,7 +18,7 @@
 obj-y += cache.o
 obj-$(CONFIG_TEGRA_CLKRST) += clock.o
 obj-$(CONFIG_TEGRA_PINCTRL) += pinmux-common.o
-obj-y += powergate.o
+obj-$(CONFIG_TEGRA_PMC) += powergate.o
 obj-y += xusb-padctl-dummy.o
 endif