ARM: tegra: cpuidle: Add missing cpuidle.h include

Some of the functions implemented are flagged as not having a prototype
defined when building with W=1. Include the header to avoid these build
warnings and add a prototype as well as a dummy implementation for the
tegra_cpuidle_pcie_irqs_in_use() function.

Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/arch/arm/mach-tegra/cpuidle.h b/arch/arm/mach-tegra/cpuidle.h
index c017dab..dd1624d 100644
--- a/arch/arm/mach-tegra/cpuidle.h
+++ b/arch/arm/mach-tegra/cpuidle.h
@@ -23,8 +23,10 @@
 int tegra30_cpuidle_init(void);
 int tegra114_cpuidle_init(void);
 void tegra_cpuidle_init(void);
+void tegra_cpuidle_pcie_irqs_in_use(void);
 #else
 static inline void tegra_cpuidle_init(void) {}
+static inline void tegra_cpuidle_pcie_irqs_in_use(void) {}
 #endif
 
 #endif