ARM: AM43xx: GP_EVM: Add support for DDR3

GP EVM has 1GB DDR3 attached(Part no: MT41K512M8RH).
Adding details for the same.
Below is the brief description of DDR3 init sequence(SW leveling):
-> Enable VTT regulator
-> Configure VTP
-> Configure DDR IO settings
-> Disable initialization and refreshes until EMIF registers are programmed.
-> Program Timing registers
-> Program leveling registers
-> Program PHY control and Temp alert and ZQ config registers.
-> Enable initialization and refreshes and configure SDRAM CONFIG register

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
diff --git a/board/ti/am43xx/mux.c b/board/ti/am43xx/mux.c
index a2d72dd..810b194 100644
--- a/board/ti/am43xx/mux.c
+++ b/board/ti/am43xx/mux.c
@@ -33,6 +33,11 @@
 	{-1},
 };
 
+static struct module_pin_mux gpio0_22_pin_mux[] = {
+	{OFFSET(ddr_ba2), (MODE(9) | PULLUP_EN)},	/* GPIO0_22 */
+	{-1},
+};
+
 void enable_uart0_pin_mux(void)
 {
 	configure_module_pin_mux(uart0_pin_mux);
@@ -42,6 +47,9 @@
 {
 	configure_module_pin_mux(mmc0_pin_mux);
 	configure_module_pin_mux(i2c0_pin_mux);
+
+	if (board_is_gpevm())
+		configure_module_pin_mux(gpio0_22_pin_mux);
 }
 
 void enable_i2c0_pin_mux(void)