Separate aidl dependencies from compiler dependencies

Both aidl and clang/gcc were putting their dependencies in the same
place.  Move aidl's dependencies to a file ending with .aidl.P rather
than the compiler's .P.

While here, inform kati that we have these special dep files.

Bug:26409006
Test: Rebuild, note both files being generated

Change-Id: I29d2eea822235d60713c2059f3a314e475eb5aa3