drm/panthor: record current and maximum device clock frequencies

In order to support UM in calculating rates of GPU utilisation, the current
operating and maximum GPU clock frequencies must be recorded during device
initialisation, and also during OPP state transitions.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923230912.2207320-3-adrian.larumbe@collabora.com