powerpc/64s: Remove WORT SPR from POWER9/10

This register is not architected and not implemented in POWER9 or 10,
it just reads back zeroes for compatibility.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Link: https://lore.kernel.org/r/20210811160134.904987-11-npiggin@gmail.com