On i.MX6 when the watchdog has resetted the system then the SRSR
register correctly shows that the watchdog has resetted the system.
This is not the desired result though, a "reset" in barebox or "reboot"
in Linux should result in "RST" as reset source. So instead of making
the SRSR register value overwrite the reset source read from the
watchdog registers, interpret the SRSR value corresponding to watchdog
reset as "lookup details in the watchdog registers".

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>