cherrypick Change-Id: I8c52dbe5ac04dfeb1b466b163ae3aec5dc401175

docs: update supports-screens doc with xlargescreens attribute...
we updated the Supporting Multiple Screens document with this attribute
for gingerbread, but this document was not updated at that time.

Change-Id: I946e7eb8b93cee1a7223d400c882f415d6045815