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>

arch/arm/mach-mmp/Kconfig

@@ -136,4 +136,7 @@ config USB_EHCI_MV_U2O
 	help
 	  Enables support for OTG controller which can be switched to host mode.
 
+config MMP_SRAM
+	bool
+
 endif

arch/arm/mach-mmp/Makefile

@@ -7,7 +7,8 @@ obj-y				+= common.o devices.o time.o
 # SoC support
 obj-$(CONFIG_CPU_PXA168)	+= pxa168.o
 obj-$(CONFIG_CPU_PXA910)	+= pxa910.o
-obj-$(CONFIG_CPU_MMP2)		+= mmp2.o sram.o
+obj-$(CONFIG_CPU_MMP2)		+= mmp2.o
+obj-$(CONFIG_MMP_SRAM)		+= sram.o
 
 ifeq ($(CONFIG_COMMON_CLK), )
 obj-y				+= clock.o