watchdog: rti_wdt: Add support for loading firmware

To avoid the need of extra boot scripting on AM65x for loading a
watchdog firmware, add the required rproc init and loading logic for the
first R5F core to the watchdog start handler. In case the R5F cluster is
in lock-step mode, also initialize the second core. The firmware itself
is embedded into U-Boot binary to ease access to it and ensure it is
properly hashed in case of secure boot.

One possible firmware source is https://github.com/siemens/k3-rti-wdt.

The board is responsible for providing the firmware as additional
loadable via the U-Boot fit image. The driver will pick up its location
from /fit-images/k3-rti-wdt-firmware then.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index eaa6f16..7d2d6ea 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -218,6 +218,26 @@
 	  Say Y here if you want to include support for the K3 watchdog
 	  timer (RTI module) available in the K3 generation of processors.
 
+if WDT_K3_RTI
+
+config WDT_K3_RTI_LOAD_FW
+	bool "Load watchdog firmware"
+	depends on REMOTEPROC
+	help
+	  Automatically load the specified firmware image into the MCU R5F
+	  core 0. On the AM65x, this firmware is supposed to handle the expiry
+	  of the watchdog timer, typically by resetting the system.
+
+config WDT_K3_RTI_FW_FILE
+	string "Watchdog firmware image file"
+	default "k3-rti-wdt.fw"
+	depends on WDT_K3_RTI_LOAD_FW
+	help
+	  Firmware image to be embedded into U-Boot and loaded on watchdog
+	  start.
+
+endif
+
 config WDT_SANDBOX
 	bool "Enable Watchdog Timer support for Sandbox"
 	depends on SANDBOX && WDT