Add support for Brillo partitioning.

To generate partition tables in the Android build system, simply add
the path to a .bpt file to the BOARD_BPT_INPUT_FILES variable.

 BOARD_BPT_INPUT_FILES += "hardware/bsp/vendor/soc/board/board-specific.bpt"

The variable BOARD_BPT_DISK_SIZE can be used to specify or override
the disk size, for example:

 BOARD_BPT_DISK_SIZE := "10 GiB"

Additional arguments to 'bpttool make_table' can be specified in the
variable BOARD_BPT_MAKE_TABLE_ARGS.

If BOARD_BPT_INPUT_FILES is set, the build system generates two files

 partition-table.img
 partition-table.bpt

in ${ANDROID_PRODUCT_OUT} using 'bpttool make_table'. The former is
the binary partition tables generated using bptool's --output_gpt
option and the latter is a JSON file generated using the --output_json
option. These files will also be put in the IMAGES/ directory of
target-files.zip when running 'm dist'.

BUG=27831397
TEST=Manually tested.

Change-Id: Iedd15354afb2dd483dcb9bc001360b2a37fd6dc0