irqdomain: Set IRQ_DOMAIN_FLAG_DESTROY_GC in __irq_domain_instantiate()

When a driver uses irq_domain_instantiate() with dgc_info to create
generic irq chips, IRQ_DOMAIN_FLAG_DESTROY_GC is required so that
irq_domain_remove() can clean up those generic chips.

All existing in-tree callers manually set this flag today, but this
pattern is error-prone. A future new caller forgetting to set the flag
would leave generic chips allocated by irq_domain_alloc_generic_chips()
leaked on domain removal.

Set IRQ_DOMAIN_FLAG_DESTROY_GC right after
irq_domain_alloc_generic_chips() succeeds inside
__irq_domain_instantiate().  This makes automatic cleanup the default
for all users that provide dgc_info via irq_domain_instantiate().

This is the correct location for the flag because:

  - irq_domain_instantiate() is a high-level wrapper which internally
    allocates the generic chips, so it should also take responsibility
    for arranging their cleanup.

  - Setting the flag in irq_domain_alloc_generic_chips() would affect
    legacy callers like __irq_alloc_domain_generic_chips(), some of
    which have custom cleanup paths that manually free the generic
    chips (e.g. gpio-tb10x does kfree(domain->gc) before
    irq_domain_remove()), leading to use-after-free.

Signed-off-by: Qingshuang Fu <fuqingshuang@kylinos.cn>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Herve Codina <herve.codina@bootlin.com>
Link: https://patch.msgid.link/20260907024046.28845-2-fuqingshuang@kylinos.cn

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