gpu: ipu-v3: Add rotation mode conversion utilities

Add two functions:

- ipu_degrees_to_rot_mode(): converts a degrees, hflip, and vflip setting
  to an IPU rotation mode.
- ipu_rot_mode_to_degrees(): converts an IPU rotation mode with given hflip
  and vflip settings to degrees.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>