ARM: keystone2: use detected ddr3a size

Because KS2 u-boot works in 32 bit address space the existing ram_size
global data field cannot be used. The maximum, which the get_ram_size()
can detect is 2GB only. The ft_board_setup() needs the actual ddr3 size
to fix up dtb.

This commit introduces the ddr3_get_size() which uses SPD data to
calculate the ddr3 size. This function replaces the "ddr3_size"
environment variable, which was used to get the SODIMM size.

For platforms, which don't have SODIMM with SPD and ddr3 is populated to
a board a simple ddr3_get_size function that returns ddr3 size has to be
implemented. See hardware-k2l.h

Signed-off-by: Vitaly Andrianov <vitalya@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/board/ti/ks2_evm/board.c b/board/ti/ks2_evm/board.c
index 7d1709c..ca668a7 100644
--- a/board/ti/ks2_evm/board.c
+++ b/board/ti/ks2_evm/board.c
@@ -146,9 +146,7 @@
 
 	ddr3a_size = 0;
 	if (lpae) {
-		env = getenv("ddr3a_size");
-		if (env)
-			ddr3a_size = simple_strtol(env, NULL, 10);
+		ddr3a_size = ddr3_get_size();
 		if ((ddr3a_size != 8) && (ddr3a_size != 4))
 			ddr3a_size = 0;
 	}