These are the kexts for ATI Mobility Radeon HD 550v/4650 (1002_9480), taken from OS X 10.9.3 (13D65). Edited by me, works also HDMI & VGA output.
Thanks bcc9 & crazybirdy - http://www.insanelymac.com/forum/topic/252061-mobility-radeon-hd-4650full-resolution-with-qe-ci-working-on-internal-lvds-screen/
Delete only AMD4600Controller.kext.
Install these two kexts with kext utility or others kext installer.
N.B. Resolution more than 1366x768 will not work.