drm/xe: Store platform name in xe_device.info

We already maintain the platform name as part of the device
descriptor, but in xe_device.info we only store platform enum,
which is not the best for use in any user-facing messages.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240521142257.756-2-michal.wajdeczko@intel.com