Add GT abstraction layer

Patch commit message + kernel doc in xe_gt_types.h + xe_device_types.h should explain rational. Also included is small patch to fix a bug where xe_hw_engines was setup for engines not present on the platform.

Per @danvet feedback, drmm_add_action_or_reset should be used for clean up but this MR doesn't do that yet. Have a follow on MR to do this but not including it in this MR to keep the review focused on the GT abstraction layer.

Currently GT instantiated in the device but could easily change this to an allocated pointer as wrappers are used to go from the device to GT and the GT to the device.