Breno observed panics when using failslab under certain conditions during
runtime:

   can not alloc irq_pin_list (-1,0,20)
   Kernel panic - not syncing: IO-APIC: failed to add irq-pin. Can not proceed

   panic+0x4e9/0x590
   mp_irqdomain_alloc+0x9ab/0xa80
   irq_domain_alloc_irqs_locked+0x25d/0x8d0
   __irq_domain_alloc_irqs+0x80/0x110
   mp_map_pin_to_irq+0x645/0x890
   acpi_register_gsi_ioapic+0xe6/0x150
   hpet_open+0x313/0x480

That's a pointless panic which is a leftover of the historic IO/APIC code
which panic'ed during early boot when the interrupt allocation failed.

The only place which might justify panic is the PIT/HPET timer_check() code
which tries to figure out whether the timer interrupt is delivered through
the IO/APIC. But that code does not require to handle interrupt allocation
failures. If the interrupt cannot be allocated then timer delivery fails
and it either panics due to that or falls back to legacy mode.

Cure this by removing the panic wrapper around __add_pin_to_irq_node() and
making mp_irqdomain_alloc() aware of the failure condition and handle it as
any other failure in this function gracefully.
Reported-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Breno Leitao <leitao@debian.org>
Tested-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Link: https://lore.kernel.org/all/ZqfJmUF8sXIyuSHN@gmail.com
Link: https://lore.kernel.org/all/20240802155440.275200843@linutronix.de