Update soong for blueprint change to allow multiple deps

Blueprint allows multiple dependencies on the same module after
https://github.com/google/blueprint/pull/210.

Fix defaults, WalkDeps can now find the same defaults module multiple
times.

Fix droiddoc, if the srcs_lib points to a lib module that is
specified multiple times, for example through explicit properties
and implicit default libraries, the srcs would be listed on the
command line multiple times.  Move srcs_lib to use its own dependency
tag.

Test: m checkbuild
Change-Id: Ia30ce83be1382820d76bca5046ad18cbffe8af1a