Replace boolean arguments with flags for bilinear fast path template

Replace boolean arguments with flags for bilinear fast path template

By replacing boolean arguments with flags, the code can be more
readable and flags can be extended to do some more things later.

Currently following flags are defined.

FLAG_NONE
    - No flags are turned on.

FLAG_HAVE_SOLID_MASK
    - Template will generate solid mask composite functions.

FLAG_HAVE_NON_SOLID_MASK
    - Template will generate bits mask composite functions.

FLAG_HAVE_SOLID_MASK and FLAG_NON_SOLID_MASK should be mutually
exclusive.