Package softdep-mga2x: Information

- check for CPUs with integrated GPU so that CPU-specific
  kernels on systems without those do not fail to install
- %preun would wipe out the payload strings from initrd.mk
  on upgrade, drop it and introduce a %post check to only
  make the changes when really required

- e2kv6: added simple-bridge, display-connector
  based on livecd vs install2 test

- renamed to softdep-mga2x (config filename adjusted accordingly)
- build for v6/v4 only (contents differ a bit; see also mcst#8392)