SystemUI: Rework SearchPanelView calculations

Make isScreenLarge calculations match how the system calculates where to put the navigation
bar. This fixes certain cases where the quick launch buttons on the glowpad of the
navigation bar is improperly oriented.

Patch set 2: The eval should be greater OR EQUAL to 600, not just greater. Also cache result
into a boolean before returning it.

Patch set 3-4: Actually cache it this time.

Patch set 5-6: Make it final.

Change-Id: I5703578b4d49a6eeab100bb23167abd5cf9a326d