intel: devinfo: store number of EUs per subslice

intel: devinfo: store number of EUs per subslice

This will be reused to store values reported by the kernel. The main
use case will be for use as the input values of the metric sets
equations for the INTEL_performance_queries extension. By storing this
information in the gen_device_info we make this non GL specific so
this can be reused by Vulkan if we ever have an equivalent extension.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>