x86/smpboot: Move synchronization masks to SMP boot code

The usage is in smpboot.c and not in the CPU initialization code.

The XEN_PV usage of cpu_callout_mask is obsolete as cpu_init() not longer
waits and cacheinfo has its own CPU mask now, so cpu_callout_mask can be
made static too.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Helge Deller <deller@gmx.de> # parisc
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck
Link: https://lore.kernel.org/r/20230512205256.091511483@linutronix.de