COMP: Support build with Slicer_BUILD_DICOM_SUPPORT "on" then "off"

In commit r21598, the option Module_ITKIODCMTK was conditionally added
depending on the value of Slicer_BUILD_DICOM_SUPPORT.

To support build tree where Slicer_BUILD_DICOM_SUPPORT is first enabled
and then disabled, the options should be directly added so that ITK
is rebuilt with the module turned off.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22368 3bd1e089-480b-0410-8dfb-8563597acbee