[ARM] Kirkwood: restrict the scope of the PCIe reset workaround

Commit 21f0ba90 "orion/kirkwood: reset PCIe unit on boot" made the
reset of the PCIe unit unconditional.  While this may fix problems on some
targets, this also causes problems on other targets.

Saeed Bishara <saeed@marvell.com> said about the original problem: "We
couln't pinpoint the root cause of this issue, actually we failed to
reproduce that issue."

So let's restrict the reset of the PCIe unit only to the target where
the original problem was observed.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>