Add a 'ubenv import' command to import environment variables from the
u-boot env into the loader(8) env (which also gets them into the kernel
env).  You can import selected variables or the whole environment.  Each
u-boot var=value becomes uboot.var=value in the loader env.  You can also
use 'ubenv show' to display uboot vars without importing them.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271285 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f