clover: Query drivers for max clock frequency

clover: Query drivers for max clock frequency

Igor Gnatenko:

v2: PIPE_COMPUTE_CAP_MAX_CLOCK_FREQUENCY instead of
    PIPE_COMPUTE_MAX_CLOCK_FREQUENCY

Bruno Jiménez:

  v3: Drivers report clock in Mhz

Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>