net: lwm2m: Add LWM2M object 9 software management

Adds support for LWM2M object 9 Software management.
This is implemented according to this release:
http://openmobilealliance.org/release/LWM2M_SWMGMT/V1_0_1-20200616-A/



Note that the XML is lacking some resources and for that reason those
resources are not included. This is a known problem by OMA and will be
fixed in a later releases.

This uses the lwm2m_pull_context to pull binaries in case
FIRMWARE_PULL_SUPPORT is enabled

Signed-off-by: Michal Ciesielski <michal.m.ciesielski@voiapp.io>