arm64: smp: honour #address-size when parsing CPU reg property

For systems where the top 32-bits of the MPIDR are all zero, we should
allow the device-tree to specify an #address-size of 0x1 for the CPU reg
property and then zero extend the value there.

Without this patch, kvmtool breaks with the recent mpidr parsing code
introduced in 4c7aa002

 ("arm64: kernel: initialise cpu_logical_map
from the DT").

Acked-by: Javi Merino <javi.merino@arm.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>