mm: rename cpu_bitmap field to flexible_array

mm: rename cpu_bitmap field to flexible_array

The cpu_bitmap flexible array now contains more than just the cpu_bitmap.
In preparation for changing the static mm_struct definitions to cover for
the additional space required, change the cpu_bitmap type from "unsigned
long" to "char", require an unsigned long alignment of the flexible array,
and rename the field from "cpu_bitmap" to "flexible_array".

Introduce the MM_STRUCT_FLEXIBLE_ARRAY_INIT macro to statically initialize
the flexible array.  This covers the init_mm and efi_mm static
definitions.

This is a preparation step for fixing the missing mm_cid size for static
mm_struct definitions.

Link: https://lkml.kernel.org/r/20251224173358.647691-3-mathieu.desnoyers@efficios.com
Fixes: af7f588d8f73 ("sched: Introduce per-memory-map concurrency ID")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Thomas Gleixner <tglx@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Aboorva Devarajan <aboorvad@linux.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Christan König <christian.koenig@amd.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Liam R . Howlett" <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Martin Liu <liumartin@google.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>