Currently, TIME CSRs are emulated only for user-only mode. This
patch add TIME CSRs emulation for privileged mode.
For privileged mode, the TIME CSRs will return value provided
by rdtime callback which is registered by QEMU machine/platform
emulation (i.e. CLINT emulation). If rdtime callback is not
available then the monitor (i.e. OpenSBI) will trap-n-emulate
TIME CSRs in software.
We see 25+% performance improvement in hackbench numbers when
TIME CSRs are not trap-n-emulated.
Backports commit c695724868ce4049fd79c5a509880dbdf171e744 from qemu