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: NAtish Patra <atish.patra@wdc.com>
Signed-off-by: NAnup Patel <anup.patel@wdc.com>
Reviewed-by: NAlexander Graf <agraf@suse.de>
Reviewed-by: NLukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>