drm/xe/query: Move timestamp reg to hwe_read_timestamp()

__read_timestamps() is actually reading the timestamp from a certain
hwe. Use it as parameter, move register declarations to be inside that
function and rename it.

Reviewed-by: Sai Teja Pottumuttu <sai.teja.pottumuttu@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241011035618.1057602-2-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>