Add both app_process[32|64] to PDK_SYMBOL_FILES_LIST

We may not be building all of them.
The platform.zip just silently ignores the nonexistent ones.
Also grep out the existing one when eastablishing the dependency in
fusion build.

Actually PDK_SYMBOL_FILES_LIST is used in 2 cases:
1) to build the symbol files into the platform.zip.
2) to establish the dependency on the symbol files
   when doing fusion build.
The previous fix only considered case 2).

Bug: 14997273
Change-Id: I028a5b6c3a3b001efac33d3f56bd2a84f532e5b3