irqchip/irq-bcm7038-l1: Guard uses of cpu_logical_map

cpu_logical_map is only defined for CONFIG_SMP builds, when we are in an
UP configuration, the boot CPU is 0.

Fixes: 6468fc18 ("irqchip/irq-bcm7038-l1: Add PM support")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200724184157.29150-1-f.fainelli@gmail.com