[U-Boot] [RFC PATCH] Provide a mechanism to avoid using #ifdef everywhere

[Harvey Chapman]

I'm not sure if this has been discussed, but I've found as a new u-boot user there are often features that require enabling other CONFIG macros that I think should just be auto-enabled as dependencies. Please keep this in mind for any future designs. For example, when enabling CONFIG_CMD_UBI and CONFIG_CMD_UBIFS, my builds failed with linker errors because I didn't know that I needed to also define CONFIG_RBTREE and CONFIG_LZO.

Thanks,
Harvey