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>