Make method names clearer (credit AOKP)

Rename isTablet() and isPhablet() to isTabletUI() and isPhabletUI()
to make the meaning clearer.
Change-Id: I7bc61b51275e4a2bdffe16a38b0b4467cc0a476a
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>