When kvm_pause is called early (from taking the rwlock), it segfaults
because the CPU array is initialized slightly later. Fix this.

This doesn't happen at the moment but the gicv2m patch will register an
MMIO region, which requires br_write_lock. gicv2m is instantiated by
kvm__arch_init from within core_init (level 0). The CPU array is
initialized later in base_init (level 1).

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>