The componentlayout form field type provides a drop down list of all available layouts for a view of an extension. If the parameter has a saved value this is selected when the page is first loaded. If not, the default value (if any) is selected.
Example XML parameter definition:
<field name="mylayout" type="componentlayout" extension="com_content" view="article" label="JFIELD_ALT_LAYOUT" useglobal="true" description="JFIELD_ALT_COMPONENT_LAYOUT" />