recipes-kernel: linux: Use the same defconfig for RK30xx and RK31xx SoCs
recipes-kernel: linux: Change the way tags are retrieved

By default the git fetcher try to find a tag attached to a branch (master for us).
This is not true with linux-next as only the current tag is attached to master,
other ones are still actives and maintained but detached. Adding argument
"nobranch=1" to SRC_URI fixes this issue. Then, we need to define the commit id
in SRCREV. In this way, we can checkout any active tag from next (as there are
present during 2 months, this is useful).
recipes-kernel: linux: Switch to lastest upstream tag