net: lwm2m: Update IPSO objects to version 1.1

[rlubos]

Zephyr LwM2M implementation has a non-standard extension, which adds the Timestamp resource to several IPSO objects: caa06c9

Currently though, all IPSO objects that utilize this feature have an updated specification version available (1.1), which extends objects with new resources, and Timestamp is one of them. This makes the non-standard Zephyr extension no longer needed.

We should drop the LWM2M_IPSO_TIMESTAMP_EXTENSIONS option, and implement the said objects in their version 1.1. The object version should be selectable with Kconfig. This will allow having the Timestamp resource available while still sticking to the standard.