powerpc/watchdog: Tweak watchdog printks

Use pr_fmt() in the watchdog code, so we don't have to say "Watchdog"
so many times.

Rather than "CPU:%d" just spell it "CPU %d", "Hard" doesn't need a
capital in the middle of a sentence, and "LOCKUP other CPUS" should be
"LOCKUP on other CPUS".

Also make it clear when a CPU self detects a lockup by spelling it
out.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>