xen/arm: Release maintenance interrupt when CPU is hot-unplugged

xen/arm: Release maintenance interrupt when CPU is hot-unplugged

When a CPU is hot-unplugged the maintenance interrupt has to be
released in order to free the memory that was allocated when the CPU
was hotplugged and interrupt requested. The interrupt was requested
using request_irq() which is called from start_secondary->
init_maintenance_interrupt. With this patch the interrupt will be
released when the CPU_DYING event is received by the callback which
is added in gic.c.

Signed-off-by: Mirela Simonovic <mirela.simonovic@aggios.com>
Acked-by: Julien Grall <julien.grall@arm.com>