Cleanup of headers, do not include headers in RAN context, CMakeLists.txt link to header only library

original motivation is to build T as lib -> through config module depended on ASN.1, slowing down build and tests

relevant changes in this MR:

• make header-only lib for ASN.1 to speed up compilation for libs with header ASN.1
• don't include ASN.1 in platform_constants.h, because this includes ASN.1 RRC everywhere
• then, forward-declaration in RC to not need to include all headers in all of OAI
• split phy_init.h in two version (for LTE, NR)
• remove most phy_vars* contents, only one phy_extern.h
• Maybe most important: refactor build_oai to build most targets in one go instead of steps, which speeds up the build
• various cleanups

• I have to take out one commit