irqchip/mvebu-gicp: Clear pending interrupts on init

When a kexec'ed kernel boots up, there might be stale unhandled interrupts
pending in the interrupt controller. These are delivered as spurious
interrupts once the boot CPU enables interrupts.

Clear all pending interrupts when the driver is initialized to prevent
these spurious interrupts from locking the CPU in an endless loop.

Signed-off-by: Elad Nachman <enachman@marvell.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250803102548.669682-2-enachman@marvell.com