[U-Boot] "make env" now requires a configured tree

[Loïc Minier]

        Hi Grant,

 "make env" worked from an unconfigured u-boot tree until
 aa701b94336b358798d676eef12a7b90bdac23f5; now it requires a config.h to
 build.

 For the Debian/Ubuntu u-boot-tools packages, we're shipping
 fw_printenv/_setenv along other tools built with no particular config
 as a convenience for Debian/Ubuntu users.  It's also used to generate
 pre-built installation media including u-boot kernel images or
 environment.

 Would you please adjust your changes not to require config.h?  If
 that's not possible for all cases, could you include some flag to build
 with defaults when config.h isn't present?

   Thanks!
-- 
Loïc Minier