OMAPDSS: add new vsync and line getter ioctls

OMAPDSS: add new vsync and line getter ioctls

OMAPFB_WAITFORVSYNC_FRAME has an int arg which is the current frame
number (both an input and output). The ioctl only waits if the passed
arg matches the current frame number, otherwise it instantly returns.
It always updates the arg to the current frame number on return.

This can be used for a reliable adaptive vsync implementation where
vsync wait will only happen if the program renders a frame faster
than it's displayed.

OMAPFB_GET_LINE_STATUS reads the line number from OMAP's DISPC hardware.
Note that the number is 0 while blanking (VFP, vsync, VBP).
When the display is off, it seem to always return 2047.