ARM: mmp: build sram driver alone

sram driver can be used by many chips besides CPU_MMP2, and so build
it alone. Also need to select MMP_SRAM for MMP_TDMA driver.

Reported-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Qiao Zhou <zhouqiao@marvell.com>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Olof Johansson <olof@lixom.net>
diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index 446687c..af36763 100644
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -289,9 +289,11 @@
 	bool "MMP Two-Channel DMA support"
 	depends on ARCH_MMP
 	select DMA_ENGINE
+	select MMP_SRAM
 	help
 	  Support the MMP Two-Channel DMA engine.
 	  This engine used for MMP Audio DMA and pxa910 SQU.
+	  It needs sram driver under mach-mmp.
 
 	  Say Y here if you enabled MMP ADMA, otherwise say N.