sr: Fix vsync logic

 * Use CLOCK_MONOTONIC to insulate from system clock changes.
 * Normalize all timespec calculations to avoid overflow/underflow.
 * Don't signal vsync if poll() fails.

Change-Id: Iedab45562d8dc472c46918fcb4b8da618f1d7bda
sr: Only use 4 items on wipe confirmation screen

 * Large fonts in Touch UI prevent more than about 7 menu lines.

Change-Id: Ic294d2db9a655db2ceeaced7a0fcd1da96fdc351