Fix parser for BOARD_BLUETOOTH_BDROID_BUILDCFG_INCLUDE_DIR

* Current parser does not support multi-directory lists, which may cause
  a build failure if BoardConfig.mk defines one.
* This CL splits the list of directories using whitespace and adds them
  individually to the include list

Bug: 34396100
Test: Code compilation, no user visible effect
Change-Id: I59e901d76d1bc20f50b54941a3007c5521ded214