libini2: Simplify using *_attr_[read|write]_all functions from libiio

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
plugins/fmcomms2_adv: Speed up loading by reading all attributes at once

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
iio_widget: Add util function iio_update_widgets_of_device

This function can be used by the plugins to update all the widgets
related to one device. This function is optimized to speed up the
update of the widgets when the network backend of libiio is used.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
plugins/fmcomms2: Speed up loading by using iio_update_widgets_of_device

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
Osc: Don't force the plugins to reload their config at startup

They already do load their config on their own in their init function.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>