Adjust where the back button is rendered for new SUW requirements.

Large screen devices in landscape mode and devices that have mostly a
square aspect ratio are undergoing a redesign in Setup wizard that makes
most screens two-pane. As part of this redesign, the back button is
aligned in this change. This change doesn't use a flag because the Setup
Wizard change is not flagged.

Fixes: 323778778
Fixes: 328017929
Test: Run Setup Wizard and see if the back button aligns with the Skip
button in two pane screens.
Flag: N/A

Change-Id: I22680f40c0ddf7cd03ab1da69406eb14184b0174
Merged-In: I22680f40c0ddf7cd03ab1da69406eb14184b0174