Added DMA support for UART4 and UART5. UART5 available only in F4x platform. Code tested on STM32F407. UART5 tested with slightly modified teshal (included in attached patch). UART4 tested with RS-485 Volz servo (http://www.volz-servos.com).
Changes does not merged in trunk because I can not test it on STM32F1x hi density platform.
Patch against latest trunk included in attach.