etamin: Rework CONFIG_NAND_CS_INIT

Enable this in the board Kconfig file, but then check for it via
CONFIG_IS_ENABLED so that it will only be true in the non-SPL case, as
is done today.  As part of this we move some defines local to where
they are used as it's board specific.

Cc: Samuel Egli <samuel.egli@siemens.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/siemens/draco/Kconfig b/board/siemens/draco/Kconfig
index a699c7d..1eb8a48 100644
--- a/board/siemens/draco/Kconfig
+++ b/board/siemens/draco/Kconfig
@@ -60,4 +60,6 @@
 config SYS_CONFIG_NAME
         default "etamin"
 
+config NAND_CS_INIT
+	def_bool y
 endif