riscv: cpu: Skip unavailable hart in the get_count() op
We should not count in hart that is marked as not available in the
device tree in riscv_cpu_get_count().
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>