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: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NQiao Zhou <zhouqiao@marvell.com>
Signed-off-by: NHaojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: NOlof Johansson <olof@lixom.net>