cypress-touchkey: new attempts at working around phantom keypress issue

- Add additional checks to verify a keypress is legit before processing
  it. This is still very hacky, and doesn't address the issue 100%, but
  is about as good as a software solution can get.

- This expands upon the original patch:
https://github.com/CyanogenMod/android_kernel_samsung_aries/commit/4afad77c61c7cb54cce293034cdb07a928f22d20

Change-Id: Ica1e1facab441ed7d07e2901c6a1f1f7b1f9d1d6