parisc: Replace cpu_up/down with add/remove_cpu

The core device API performs extra housekeeping bits that are missing
from directly calling cpu_up/down.

See commit a6717c01 ("powerpc/rtas: use device model APIs and
serialization during LPM") for an example description of what might go
wrong.

This also prepares to make cpu_up/down a private interface for anything
but the cpu subsystem.

Acked-by: Helge Deller <deller@gmx.de>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
CC: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
CC: Helge Deller <deller@gmx.de>
CC: Richard Fontana <rfontana@redhat.com>
CC: Armijn Hemel <armijn@tjaldur.nl>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: linux-parisc@vger.kernel.org
CC: linux-kernel@vger.kernel.org