sparc: 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: David S. Miller <davem@davemloft.net>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Bjorn Helgaas <bhelgaas@google.com>
CC: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Sakari Ailus <sakari.ailus@linux.intel.com>
CC: sparclinux@vger.kernel.org
CC: linux-kernel@vger.kernel.org