ice: introduce ice_base_incval function

A future change will add additional possible increment values for the
E822 device support. To handle this, we want to look up the increment
value to use instead of hard coding it to the nominal value for E810
devices. Introduce ice_base_incval as a function to get the best nominal
increment value to use.

For now, it just returns the E810 value, but will be refactored in the
future to look up the value based on the device type and configured
clock frequency.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>