IMX: Fix changing resolutions

Background:
 - imx6 as only egl driver is destroying nativedisplay on resolution change
 - xbmc's EGL code is not aware of this change (pointer to EGLDisplay can change but xbmc uses old pointer  which was obtained on EGL init. in such case EGL properly  throws error 300b - bad window - which comes from recreating new window on BAD display)
 - InitDisplay() is refreshing display pointer (and running eglInitialize() has no effect on already initialised display)

Special thanks to Matus Kral @mk01 from the xbian project for debugging and finding this fix. Highly appreciated.

@smallint @wolfgar For review please.