According to the PPC reference implementation the udelay() function is
responsible for resetting the watchdog timer as frequently as needed.
Most other architectures do not meet that requirement, so long-running
operations might result in a watchdog reset.
This patch adds a generic udelay() function which takes care of
resetting the watchdog before calling an architecture-specific
Signed-off-by: Ingo van Lil <email@example.com>