ARM: mark empty gpio.h files empty

It is generally a better idea to make intentionally empty files
contain the human-readable /* empty */ comment, also it makes
the files play nice with "make distclean".

Reported-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/arch/arm/mach-lpc32xx/include/mach/gpio.h b/arch/arm/mach-lpc32xx/include/mach/gpio.h
index e69de29..40a8c17 100644
--- a/arch/arm/mach-lpc32xx/include/mach/gpio.h
+++ b/arch/arm/mach-lpc32xx/include/mach/gpio.h
@@ -0,0 +1 @@
+/* empty */
diff --git a/arch/arm/mach-tegra/include/mach/gpio.h b/arch/arm/mach-tegra/include/mach/gpio.h
index e69de29..40a8c17 100644
--- a/arch/arm/mach-tegra/include/mach/gpio.h
+++ b/arch/arm/mach-tegra/include/mach/gpio.h
@@ -0,0 +1 @@
+/* empty */
diff --git a/arch/arm/mach-u300/include/mach/gpio.h b/arch/arm/mach-u300/include/mach/gpio.h
index e69de29..40a8c17 100644
--- a/arch/arm/mach-u300/include/mach/gpio.h
+++ b/arch/arm/mach-u300/include/mach/gpio.h
@@ -0,0 +1 @@
+/* empty */