lib: sbi_init: Don't allow HARTID greater than SBI_HARTMASK_MAX_BITS

We only allow HARTs with HARTID less than SBI_HARTMASK_MAX_BITS in
sbi_init() function so that sbi_hartmask can safely used across
OpenSBI sources.

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