drivers: ddr: Add DDR2 SDRAM controller driver for Microchip PIC32.

This driver initializes PIC32 DDR2 SDRAM controller and internal DDR2 Phy module.
DDR2 controller operates in half-rate mode (upto 533MHZ frequency).

Signed-off-by: Paul Thacker <paul.thacker@microchip.com>
Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/mips/mach-pic32/include/mach/ddr.h

@@ -0,0 +1,32 @@
+/*
+ * (c) 2015 Purna Chandra Mandal <purna.mandal@microchip.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ *
+ */
+
+#ifndef __MICROCHIP_PIC32_DDR_H
+#define __MICROCHIP_PIC32_DDR_H
+
+/* called by initdram() function */
+void ddr2_phy_init(void);
+void ddr2_ctrl_init(void);
+phys_size_t ddr2_calculate_size(void);
+
+/* Maximum number of agents */
+#define NUM_AGENTS		5
+
+/* Board can provide agent specific parameters for arbitration by
+ * filling struct ddr2_arbiter_params for all the agents and
+ * implementing board_get_ddr_arbiter_params() to return the filled
+ * structure.
+ */
+struct ddr2_arbiter_params {
+	u32 min_limit;	/* min bursts to execute per arbitration */
+	u32 req_period; /* request period threshold for accepted cmds */
+	u32 min_cmd_acpt; /* min number of accepted cmds */
+};
+
+const struct ddr2_arbiter_params *board_get_ddr_arbiter_params(void);
+
+#endif /* __MICROCHIP_PIC32_DDR_H */