driver-core: improve driver binding documentation

The driver binding documentation (still) mentions that "When a driver is
attached to a device, the device is inserted into the driver's list of
devices.".

While it is true that the driver-core keeps track of all the devices
that are attached to a driver, this is purely for internal purposes
(i.e. it is an implementation detail) and has no relevance for user
facing documentation.

In fact, it is even misleading, since it could be read as if it were
valid for driver implementations to keep track of all the devices bound
to it.

Instead, drivers operate on a per-device basis, with a separate
per-device instance created when the driver is bound to a device.

Hence, remove the mention of a driver's list of devices and instead add
some documentation of the relationship between drivers and devices.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260115215718.6405-1-dakr@kernel.org>