dm: core: Provide fallbacks for ofnode_conf_read_...
Because fdt_get_config_str et al. were moved/renamed to
ofnode_conf_read_str, they now depend on CONFIG_DM as well as
CONFIG_OF_CONTROL. Add some fallback implementations, preventing a
linker error when CONFIG_SPL_OF_CONTROL and CONFIG_SPL_ENV_IS_IN_MMC are
enabled and CONFIG_SPL_DM is disabled.
Fixes: 7de8bd03c3 ("treewide: fdt: Move fdt_get_config_... to ofnode_conf_read...") Signed-off-by: Sean Anderson <sean.anderson@seco.com>