lib: sbi: Remove MCOUNTINHIBT hart feature

If a hart implements privileged spec v1.11 (or higher) then we can
safely assume that mcountinhibit CSR is present and we don't need
MCOUNTINHIBT as a hart feature.

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