powerpc/mm/highmem: use __set_pte_at() for kmap_local()

The original PowerPC highmem mapping function used __set_pte_at() to
denote that the mapping is per CPU.  This got lost with the conversion
to the generic implementation.

Override the default map function.

Link: https://lkml.kernel.org/r/20210112170411.281464308@linutronix.de
Fixes: 47da42b2

 ("powerpc/mm/highmem: Switch to generic kmap atomic")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Paul Cercueil <paul@crapouillou.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>