drivers: reset: Add a managed API to get reset controllers from the DT

Add managed functions to get a reset_ctl from the device-tree, based on a
name or an index.
Also add a managed functions to get a reset_ctl_bulk (array of reset_ctl)
from the device-tree.

When the device is unbound, the reset controllers are automatically
released and the data structure is freed.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>