tegra: tegra124: Add a PMC syscon driver

The PMC can be modelled as a syscon peripheral. Add a driver for this
so that it can be accessed by drivers when needed. Enable it for tegra124
boards.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-on: Beaver, Jetson-TK1
Tested-by: Stephen Warren <swarren@nvidia.com>

arch/arm/include/asm/arch-tegra/tegra.h

@@ -97,6 +97,11 @@ enum {
 	TEGRA_SOC_UNKNOWN	= -1,
 };
 
+/* Tegra system controller (SYSCON) devices */
+enum {
+	TEGRA_SYSCON_PMC,
+};
+
 #else  /* __ASSEMBLY__ */
 #define PRM_RSTCTRL		NV_PA_PMC_BASE
 #endif