net: fec_mpc52xx: Replace in_interrupt() usage

The usage of in_interrupt() in drivers is phased out and Linus clearly
requested that code which changes behaviour depending on context should
either be seperated or the context be conveyed in an argument passed by the
caller, which usually knows the context.

mpc52xx_fec_stop() uses in_interrupt() to check if it is safe to sleep. All
callers run in well defined contexts.

Pass an argument from the callers indicating whether it is safe to sleep.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>