package/poppler: bump version to 0.32.0

This commit also adds an optional dependency on openjpeg: if
--enable-openjpeg=none is not passed, poppler assumes openjpeg is
available.

[Thomas:
  - add optional dependency on openjpeg instead of mandatory
    dependency.
  - remove --enable-xpdf-headers, since there was no justification for
    it.]

Signed-off-by: Olivier Schonken <olivier.schonken@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>