Each of the sibling CPUs in a cluster uses the same clustermask. The first
CPU in a cluster will need a new clustermask allocated, while subsequent
siblings will use the same clustermask as the first.

However, the CPU being brought up cannot yet perform memory allocations
at the point that this occurs in init_x2apic_ldr().

So at present, the alloc_clustermask() function allocates a clustermask
just in case it's needed, storing it in the global cluster_hotplug_mask.
A CPU which is the first sibling of a cluster will "take" it from there
and set cluster_hotplug_mask to NULL, in order for alloc_clustermask()
to allocate a new one before bringing up the next CPU.

To facilitate parallel bringup of CPUs in future, switch to a model
where alloc_clustermask() prepopulates the clustermask in the per_cpu
data for each present CPU in the cluster in advance. All that the CPU
needs to do for itself in init_x2apic_ldr() is set its own bit in that
mask.

The 'node' and 'clusterid' members of struct cluster_mask are thus
redundant, and it can become a simple struct cpumask instead.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Usama Arif <usama.arif@bytedance.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Kim Phillips <kim.phillips@amd.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Link: https://lore.kernel.org/r/20230316222109.1940300-2-usama.arif@bytedance.com