ice: track hardware stat registers past rollover

Currently, ice_stat_update32 and ice_stat_update40 will limit the
value of the software statistic to 32 or 40 bits wide, depending on
which register is being read.

This means that if a driver is running for a long time, the displayed
software register values will roll over to zero at 40 bits or 32 bits.

This occurs because the functions directly assign the difference between
the previous value and current value of the hardware statistic.

Instead, add this value to the current software statistic, and then
update the previous value.

In this way, each time ice_stat_update40 or ice_stat_update32 are
called, they will increment the software tracking value by the
difference of the hardware register from its last read. The software
tracking value will correctly count up until it overflows a u64.

The only requirement is that the ice_stat_update functions be called at
least once each time the hardware register overflows.

While we're fixing ice_stat_update40, modify it to use rd64 instead of
two calls to rd32. Additionally, drop the now unnecessary hireg
function parameter.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>