build: separate dist tools and ota tools

aapt is not needed for a dist build and not available in a pdk dist
build.  Create a new list DISTTOOLS that dist builds depends on,
and change OTATOOLS to be DISTTOOLS plus aapt, which is build by
make otatools.

Change-Id: I9a39020640b0e2cade8073aa14ee2ada9a20d78b