Add .hpp files to sgrep and treegrep

There are plenty of .hpp files in the AOSP sources.

    $ find . -name \*.hpp | wc -l
    2430

They were already grepped in cgrep(), but were missing in
sgrep and treegrep.

Test: manual - run the script

Change-Id: I1fb3f576f6cdcc2b492e2beadf11ced98cb3938e