powerpc/configs: Explicitly drop CONFIG_INPUT_MOUSEDEV

In commit 73d8ef76 ("Input: mousedev - stop offering PS/2 to userspace by
default") (Jan 2017), CONFIG_INPUT_MOUSEDEV was switched from default y to
default n, with the explanation:

  Evdev interface has been available for many years and by now everyone
  is switched to using it, so let's stop offering /dev/input/mouseN
  and /dev/psaux by default.

We had a number of configs which had it enabled, but going by the above
explanation probably don't need it enabled anymore.

So drop the last remnants of it from our defconfigs.

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