lib: Implement Hart State Management (HSM) SBI extension

This patch adds support HSM extension. The specification is available
at https://github.com/riscv/riscv-sbi-doc

.

It allows to implement hart hotplug and fixed ordered hart booting in
supervisor.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>