lib: sbi: Detect AIA CSRs at boot-time

We extend HART feature detection to discover AIA CSRs at boot-time.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>