drm/xe: Add helper to return any available hw engine

Get the first available engine from a gt, which helps in the case any
engine serves as a context, like when reading RING_TIMESTAMP.

Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240517204310.88854-8-lucas.demarchi@intel.com


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