dm: pmic: ignore disabled node in pmic_bind_children

Ignore the disabled children node in pmic_bind_children() so the
disabled regulators in device tree are not registered.

This patch is based on the dm_scan_fdt_node() code - only the
activated nodes are bound -  and it solves possible issue when a
deactivated regulator is bound, error for duplicated regulator name
for example.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>