MAINTAINERS: Add FDMA driver files to STi section.

This patch adds the FDMA driver files to the STi
section of the maintainers file.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>