lib: sbi: Detect and print privileged spec version

It is possible to guess privileged spec versions based on the CSRs
that where introduced in different privileged spec versions. In
future, if we are not able guess privileged spec version then we
can have platform provide it.

We add privileged spec version as per-hart feature and try to guess
it based on presence of mcounteren, mcountinhibit, and menvcfg CSRs.

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