net: lwm2m: Re-order lwm2m object structs for memory alignment

Let's optimize the order of the following structures to account for
memory alignment:
lwm2m_engine_obj
lwm2m_engine_res_inst
lwm2m_output_context
lwm2m_output_context

Tested building for nrf52_blenano hardware:
SRAM usage before patch: 38240 B
SRAM usage after patch: 37952 B

Signed-off-by: Michael Scott <michael@opensourcefoundries.com>