Convert ARCH_OMAP2PLUS boards' CONFIG_SYS_TEXT_BASE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_TEXT_BASE

The includes, whitelist, etc. were left for now but I don't get any
build errors or warnings on the omap3_logic_defconfig or
am3517_evm_defconfig builds I tried.

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/am335x_evm_norboot_defconfig b/configs/am335x_evm_norboot_defconfig
index 9e61728..73354f4 100644
--- a/configs/am335x_evm_norboot_defconfig
+++ b/configs/am335x_evm_norboot_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 # CONFIG_SYS_THUMB_BUILD is not set
 CONFIG_ARCH_OMAP2PLUS=y
+CONFIG_SYS_TEXT_BASE=0x08000000
 CONFIG_TI_COMMON_CMD_OPTIONS=y
 CONFIG_AM33XX=y
 CONFIG_NOR=y