powerpc/64s/exceptions: Use keyword params to shorten arg lists

The argument lists for the INT_HANDLER macro are getting a bit
unwieldy. Use keyword parameters with default values to shorten them.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190830011426.16810-1-mpe@ellerman.id.au