cpu: Bind timer driver for boot hart

cpu: Bind timer driver for boot hart

Currently, timer driver is bound only for hart0.

There is no mandatory requirement that hart0 should always
come up. In fact, HiFive Unleashed SoC hart0 doesn't boot
in S-mode because it only has M-mode.

The timer driver should be bound for boot hart.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>