watchdog: Move watchdog_dev to data section (BSS may not be cleared)

This patch moves all instances of static "watchdog_dev" declarations to
the "data" section. This may be needed, as the BSS may not be cleared
in the early U-Boot phase, where watchdog_reset() is already beeing
called. This may result in incorrect pointer access, as the check to
"!watchdog_dev" in watchdog_reset() may not be true and the function
may continue to run.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: "Marek Behún" <marek.behun@nic.cz>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Tested-by: Michal Simek <michal.simek@xilinx.com> (on zcu100)
Reviewed-by: Michal Simek <michal.simek@xilinx.com>

arch/mips/mach-mt7620/cpu.c

@@ -70,7 +70,7 @@ int print_cpuinfo(void)
 }
 
 #ifdef CONFIG_WATCHDOG
-static struct udevice *watchdog_dev;
+static struct udevice *watchdog_dev __attribute__((section(".data"))) = NULL;
 
 /* Called by macro WATCHDOG_RESET */
 void watchdog_reset(void)