ARM: tegra: Guard clock code with a Kconfig symbol

Clock 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 d4b4666..0e812818 100644
--- a/arch/arm/mach-tegra/Makefile
+++ b/arch/arm/mach-tegra/Makefile
@@ -16,7 +16,7 @@
 obj-y += ap.o
 obj-y += board.o board2.o
 obj-y += cache.o
-obj-y += clock.o
+obj-$(CONFIG_TEGRA_CLKRST) += clock.o
 obj-y += pinmux-common.o
 obj-y += powergate.o
 obj-y += xusb-padctl-dummy.o