env: Allow to set default_environment[] from board code via compile option DEFAULT_ENV_IS_RW

This change allows board code to modify default_environment[] array when
compile option DEFAULT_ENV_IS_RW is specified in board config file.

Some board default variables depend on runtime configuration which is not
known at compile time. Therefore allow to set default_environment[] array
as non-const and allow board code to modify it when it is needed.
Signed-off-by: NPali Rohár <pali@kernel.org>
Acked-by: NAndre Heider <a.heider@gmail.com>

include/env_default.h

@@ -19,6 +19,8 @@ env_t embedded_environment __UBOOT_ENV_SECTION__(environment) = {
 	{
 #elif defined(DEFAULT_ENV_INSTANCE_STATIC)
 static char default_environment[] = {
+#elif defined(DEFAULT_ENV_IS_RW)
+uchar default_environment[] = {
 #else
 const uchar default_environment[] = {
 #endif

include/env_internal.h

@@ -111,7 +111,11 @@ typedef struct environment_s {
 extern env_t embedded_environment;
 #endif /* ENV_IS_EMBEDDED */
 
+#ifdef DEFAULT_ENV_IS_RW
+extern unsigned char default_environment[];
+#else
 extern const unsigned char default_environment[];
+#endif
 
 #ifndef DO_DEPS_ONLY