exynos5420/kirby: necessary updates for DRAM

This updates DRAM usage for Kirby so that we can actually
use the available 3.5GB:

- The chips on Kirby have 16 row address lines.
- CONFIG_DRAM_SIZE_MB should be 3584 (4096-512).
- We use 2 DMC channels on Kirby (each with 2GB).

Signed-off-by: David Hendricks <dhendrix@chromium.org>
BUG=chrome-os-partner:22144
BRANCH=none
TEST=built and booted (sorta) on Kirby, mem test succeeds

Change-Id: I86d1a96d0d1a028587f7655f8de5a2e52165e9d2
Reviewed-on: https://chromium-review.googlesource.com/167489
Commit-Queue: David Hendricks <dhendrix@chromium.org>
Tested-by: David Hendricks <dhendrix@chromium.org>
Reviewed-by: ron minnich <rminnich@chromium.org>

src/cpu/samsung/exynos5420/setup.h

@@ -136,6 +136,7 @@ struct exynos5_phy_control;
 #define DMC_MEMCONFIGx_CHIP_COL_10              (3 << 8)
 #define DMC_MEMCONFIGx_CHIP_ROW_14              (2 << 4)
 #define DMC_MEMCONFIGx_CHIP_ROW_15              (3 << 4)
+#define DMC_MEMCONFIGx_CHIP_ROW_16              (4 << 4)
 #define DMC_MEMCONFIGx_CHIP_BANK_8              (3 << 0)
 
 #define DMC_MEMBASECONFIGx_CHIP_BASE(x)         (x << 16)