Revert "powerpc/powernv: Fundamental reset on PLX ports"

This reverts commit b2b5efcf.

This code was way too board specific, there are quirks as to how
the PERST line is wired on different boards, we'll have to revisit
this using/creating appropriate firmware interfaces.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>