omap3: Define DRAM banks number in Kconfig instead of defconfigs

The number of DRAM banks was defined to the same value in each OMAP3
board defconfig, which is expected and hardcoded in the code. Move the
common definition to the Kconfig option declaration instead.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Reviewed-by: Tom Rini <trini@konsulko.com>
Tested-by: Derald D. Woods <woods.technical@gmail.com>
diff --git a/Kconfig b/Kconfig
index 69e8b17..8b7b213 100644
--- a/Kconfig
+++ b/Kconfig
@@ -209,6 +209,7 @@
 config NR_DRAM_BANKS
 	int "Number of DRAM banks"
 	default 1 if ARCH_SUNXI || ARCH_OWL
+	default 2 if OMAP34XX
 	default 4
 	help
 	  This defines the number of DRAM banks.