Allow whitspace to appear between device name and unit number in loaderdev.
This allows the same value to be used in u-boot commands and the loaderdev
env var that gets passed to ubldr, for example 'fatload mmc 1 ${bootfile}".


git-svn-id: svn+ssh://svn.freebsd.org/base/head@276026 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f