fdperf: improve reads of counter values

The counter values on Adreno are 64-bit values, but only their lower
32 bits have been read until now.

This change switches to reading the complete 64-bit value, storing that
value and the delta against the previous value for each counter. Similar is
done for time values, namely storing the time value and the delta against
the previous value (in microseconds) for each counter. The deltas are then
used to compute the counter change per second, as was done before.

In curses UI, an early sampling is done during setup in order to avoid
artificially-large values popping up in the first update due to the deltas
being calculated to initially-zero values.

Signed-off-by: Zan Dobersek <zdobersek@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27483>