mailbox: Use irq_update_affinity_hint()

The driver uses irq_set_affinity_hint() to:

  - Set the affinity_hint which is consumed by the userspace for
    distributing the interrupts

  - Enforce affinity

As per commit 6ac17fe8 ("mailbox: bcm-flexrm-mailbox: Set IRQ affinity
hint for FlexRM ring IRQs") the latter is done to ensure that the FlexRM
ring interrupts are evenly spread across all available CPUs. However, since
commit a0c9259d ("irq/matrix: Spread interrupts on allocation") the
spreading of interrupts is dynamically performed at the time of allocation.
Hence, there is no need for the drivers to enforce their own affinity for
the spreading of interrupts.

Also, irq_set_affinity_hint() applying the provided cpumask as an affinity
for the interrupt is an undocumented side effect. To remove this side
effect irq_set_affinity_hint() has been marked as deprecated and new
interfaces have been introduced. Hence, replace the irq_set_affinity_hint()
with the new interface irq_update_affinity_hint() that only sets the
affinity_hint pointer.

Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Jassi Brar <jaswinder.singh@linaro.org>
Link: https://lore.kernel.org/r/20210903152430.244937-11-nitesh@redhat.com