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>

lib/sbi/objects.mk

@@ -18,6 +18,7 @@ libsbi-objs-y += sbi_ecall_base.o
 libsbi-objs-y += sbi_ecall_legacy.o
 libsbi-objs-y += sbi_ecall_replace.o
 libsbi-objs-y += sbi_ecall_vendor.o
+libsbi-objs-y += sbi_ecall_hsm.o
 libsbi-objs-y += sbi_emulate_csr.o
 libsbi-objs-y += sbi_fifo.o
 libsbi-objs-y += sbi_hfence.o