Soong: Add synopsis to ndk_* modules.

Added synopsis to the following modules under cc package:
    * ndk_headers
    * ndk_library
    * versioned_ndk_headers
    * preprocessed_ndk_headers

Bug: b/128337482
Test: Generated the documentation and verified that the synopsis was
added to each of the module.

Change-Id: I2146919528cf039ed9327b3358de5b1bdb28275a