powerpc/mpc8xxx: Add memory reset control

JEDEC spec requires the clocks to be stable before deasserting reset
signal for RDIMMs. Clocks start when any chip select is enabled and
clock control register is set. This patch also adds the interface to
toggle memory reset signal if needed by the boards.

Signed-off-by: York Sun <yorksun@freescale.com>
diff --git a/board/freescale/common/qixis.c b/board/freescale/common/qixis.c
index 40ce6b0..a49e300 100644
--- a/board/freescale/common/qixis.c
+++ b/board/freescale/common/qixis.c
@@ -107,6 +107,26 @@
 	return buf;
 }
 
+#ifdef QIXIS_RST_FORCE_MEM
+void board_assert_mem_reset(void)
+{
+	u8 rst;
+
+	rst = QIXIS_READ(rst_frc[0]);
+	if (!(rst & QIXIS_RST_FORCE_MEM))
+		QIXIS_WRITE(rst_frc[0], rst | QIXIS_RST_FORCE_MEM);
+}
+
+void board_deassert_mem_reset(void)
+{
+	u8 rst;
+
+	rst = QIXIS_READ(rst_frc[0]);
+	if (rst & QIXIS_RST_FORCE_MEM)
+		QIXIS_WRITE(rst_frc[0], rst & ~QIXIS_RST_FORCE_MEM);
+}
+#endif
+
 void qixis_reset(void)
 {
 	QIXIS_WRITE(rst_ctl, QIXIS_RST_CTL_RESET);