RGB565 works correctly only on little endian surface

After trying big endian framebuffer in i.MX6 and little endian drm framebuffer in i.MX8, it seems that RGB565 only works correctly with little endian surface format.

The easy fix is to rename the format to RGB565_LE. If big endian format is needed, then one qToBigEndian() call is needed in blitting.