linux-imx

MLK-16804-06 driver: soc: Optimize the DDR frequency in audio playback case

If audio device is the only that access to ddr memory, the DDR
frequency can be reduce to 25MHz to save power. when DDR run in
25MHz frequency, the memory bandwidth is about 66MB/s, it can
meet the performance requirement for audio only case.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
Reviewed-by: Anson Huang <anson.huang@nxp.com>
(cherry picked from commit 7c2389b6dca053ae4b4a56b3588978909769008c)