Build fixes.

- Fix paths that point outside the kernel tree. Dependencies outside the
  kernel tree were imported into the kernel tree (see import manifest).

- Add symlinks to net/bridge/br_{public,private}.h. Quantenna drivers
  #include linux/net/bridge/br_{public,private}.h, which only works in
  the SDK due to some gcc -I mischief. The "linux" directory actually
  resolves to $SDK_DIR/linux, not the usual

- Move -I flags from driver-specific Makefiles to the top-level
  arc/arc/Makefile. This allows the includes to be shared with

Some of these changes are extracted from go/fibercl/65615.

Change-Id: I7d0c16d25500540079ff8f334538f74e3e142d7f
10 files changed