nexmon, gcc plugin: up to now, it was not possible to place flash patches in multiple files and it was also not always working to use the targetregion pragma in multiple C files. In this commit we heavily rewrote our gcc plugin. It now produces an intermediate nexmon.generated.pre file that contains information about functions, variables and section that should be placed into the firmware. Then we call a couple of awk commands to produce nexmon.generated.mk, nexmon.generated.ld, flashpatches.generated.mk and flashpatches.generated.ld files which will be used for linking and patching the firmware binary. The *.generated.mk/ld files are similar to the ones used before, but now the regions are gathered at the end and sorted by name as well.