lib: sbi_ecall_legacy: Use sbi_hsm_hart_started_mask() API

This patch replaces use of sbi_hart_available_mask() API with
sbi_hsm_hart_started_mask API.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>