Move clock and smartspace complications down.

By default the home controls chip and smartspace, being on the bottom
row, are aligned at the bottom. In order for them to be center aligned,
a bottom margin is added to the home controls chip.

Test: atest ComplicationLayoutParamsTest
Test: atest ComplicationLayoutEngineTest
Test: https://screenshot.googleplex.com/7A6MSW29EjfgdYs
Bug: 257553229
Change-Id: Ifeb43149768651f6383c286023369029a6704e33