arm64: zynqmp: spl: install a PMU firmware config object at runtime

Optionally allow U-Boot to load a configuration object into the Power
Management Unit (PMU) firmware on Xilinx ZynqMP.

The configuration object is required by the PMU FW to enable most SoC
peripherals. So far the only way to boot using U-Boot SPL was to hard-code
the configuration object in the PMU firmware. Allow a different boot
process, where the PMU FW is equal for any ZynqMP chip and its
configuration is passed at runtime by U-Boot SPL.

All the code for Inter-processor communication with the PMU is isolated in
a new file (pmu_ipc.c). The code is inspired by the same feature as
implemented in the Xilinx First Stage Bootloader (FSBL) and Arm Trusted
Firmware:

 * https://github.com/Xilinx/embeddedsw/blob/fb647e6b4c00f5154eba52a88b948195b6f1dc2b/lib/sw_apps/zynqmp_fsbl/src/xfsbl_misc_drivers.c#L295
 * https://github.com/ARM-software/arm-trusted-firmware/blob/c48d02bade88b07fa7f43aa44e5217f68e5d047f/plat/xilinx/zynqmp/pm_service/pm_api_sys.c#L357

SPL logs on the console before loading the configuration object:

  U-Boot SPL 2019.07-rc1-00511-gaec224515c87 (May 15 2019 - 08:43:41 +0200)
  Loading PMUFW cfg obj (2008 bytes)
  EL Level:	EL3
  ...

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/mach-zynqmp/Kconfig b/arch/arm/mach-zynqmp/Kconfig
index 9bb5a5c..6cf17eb 100644
--- a/arch/arm/mach-zynqmp/Kconfig
+++ b/arch/arm/mach-zynqmp/Kconfig
@@ -65,6 +65,24 @@
 	  Include external PMUFW (Platform Management Unit FirmWare) to
 	  a Xilinx bootable image (boot.bin).
 
+config ZYNQMP_SPL_PM_CFG_OBJ_FILE
+	string "PMU firmware configuration object to load at runtime by SPL"
+	depends on SPL
+	help
+	  Path to a binary PMU firmware configuration object to be linked
+	  into U-Boot SPL and loaded at runtime into the PMU firmware.
+
+	  The ZynqMP Power Management Unit (PMU) needs a configuration
+	  object for most SoC peripherals to work. To have it loaded by
+	  U-Boot SPL set here the file name (absolute path or relative to
+	  the top source tree) of your configuration, which must be a
+	  binary blob. It will be linked in the SPL binary and loaded
+	  into the PMU firmware by U-Boot SPL during board
+	  initialization.
+
+	  Leave this option empty if your PMU firmware has a hard-coded
+	  configuration object or you are loading it by any other means.
+
 config ZYNQMP_USB
 	bool "Configure ZynqMP USB"