irqchip/armada-370-xp: Fix reenabling last per-CPU interrupt

The number of per-CPU interrupts is 29 (0 to 28). This is described by
the constant MPIC_MAX_PER_CPU_IRQS, set to 28 (the maximum per-CPU
interrupt).

Commit 0fa4ce74 ("irqchip/armada-370-xp: Re-enable per-CPU
interrupts at resume time") used the constant incorrectly in the
for-loop, it used the operator < instead of <=, causing it to iterate
only the first 28 interrupts (0 to 27), ignoring the last, 28th,
per-CPU interrupt.

To avoid this kind of confusions, fix this issue by renaming the constant
to MPIC_PER_CPU_IRQS_NR and set it to 29, the number of per-CPU IRQs.
Update its use in mpic_is_percpu_irq() accordingly.

Fixes: 0fa4ce74 ("irqchip/armada-370-xp: Re-enable per-CPU interrupts at resume time")
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable+noautosel@kernel.org> # The 29th interrupt is not used in any device-tree