lib: sbi_hart: move hart_features struct to a public location

Platforms may need to override auto-detected hart features
in their override functions. So move the hart_features
struct to the sbi_hart.h header allowing us to pass it over
to platform-handlers.

Suggested-by: Atish Patra <atishp@atishpatra.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>