gallium/hud: use double values for all graphs

gallium/hud: use double values for all graphs

The fps graph for example calculates the fps as double with small
variations based on when query_new_value() is called, which causes
many values to be truncated on the cast to uint64_t.

The HUD internally stores the values as double, so just use double
everywhere instead of fixing this with rounding. Using doubles also
allows the hud to show small variations instead of being clamped to
discrete values.

v2: Don't print decimals in the dump file when not necessary
Signed-off-by: Christoph Haag <haagch+mesadev@frickel.club>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>