ARM: tegra: Guard GP pad control code with a Kconfig symbol

The GP pad control 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 0e812818..69f802c 100644
--- a/arch/arm/mach-tegra/Makefile
+++ b/arch/arm/mach-tegra/Makefile
@@ -13,7 +13,7 @@
 obj-$(CONFIG_CMD_ENTERRCM) += cmd_enterrcm.o
 endif
 
-obj-y += ap.o
+obj-$(CONFIG_TEGRA_GP_PADCTRL) += ap.o
 obj-y += board.o board2.o
 obj-y += cache.o
 obj-$(CONFIG_TEGRA_CLKRST) += clock.o