This adds some additional DT labels which are handy when referring
to the nodes in derived DTS(I) files. It will also make the
definitions more consistent, e.g. by adding gsbi2_serial and
gsbi5_serial where we previously "only" had gsbi4_serial defined.

While at it, add missing spaces after some DT labels and remove one
useless empty line.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Link: https://lore.kernel.org/r/20200902165159.7733-1-freifunk@adrianschmutzler.deSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>