Convert CONFIG_SPL_BOARD_INIT to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_BOARD_INIT

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
[trini: Update the Kconfig logic]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/a3m071_defconfig b/configs/a3m071_defconfig
index 8d636e0..a461b80 100644
--- a/configs/a3m071_defconfig
+++ b/configs/a3m071_defconfig
@@ -10,6 +10,7 @@
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_SPL=y
+CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_SPL_OS_BOOT=y