There are currently two versions of IGEP v2 board, this patch introduces a
function to detect the hardware revision of IGEP board.

  --------------------------
 | Id. | Hw Rev. | GPIO 28  |
  --------------------------
 |  0  |   B/C   |   high   |
 |  1  |   C     |   low    |
  --------------------------
Signed-off-by: NEnric Balletbo i Serra <eballetbo@gmail.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>