include: Simple hartmask library

We add a simple hartmask library to create and maintain HART mask
in different parts of OpenSBI sources. This new library is build
as wrapper library on-top-of bitmap library.

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>