drm/xe/uapi: Add block diagram of a device

In order to make proper use the uAPI, a prerequisite is to understand
some key concepts about the discrete GPU devices which are supported
by the Xe driver. For example, some structs defined in the uAPI are an
abstraction of a hardware component with a specific role.

This diagram helps to build a mental representation of a device how it
is seen by the Xe driver. As written in the documentation, it does not
intend to be a literal representation of an existing device. A lot
more information could be added but the intention for the overview is
to keep it simple, and go into detail as needed in other sections.

v2: Add GT1 inside Tile0 (José Roberto de Souza)

Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Acked-by: José Roberto de Souza <jose.souza@intel.com>
Acked-by: Mateusz Naklicki <mateusz.naklicki@intel.com>
Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>