drm/xe/guc: Add support for G2G communications

drm/xe/guc: Add support for G2G communications

Some features require inter-GuC communication channels on multi-tile
devices. So allocate and enable such.

v2: Correct use of xe_bo_get/put (review feedback from Matthew Brost)
Add extra assert, re-order a calculation for better clarity and add
comments to slot calculation (review feedback from Daniele). Also
slightly re-work the slot calc to avoid code duplication.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241120000222.204095-3-John.C.Harrison@Intel.com