EFI: don't call printf after ExitBootServices, since it uses Boot Services

ExitBootServices terminates all boot services including console access.
Attempting to call printf afterwards can result in a crash, depending on the
implementation.

Move any printf statements to before we call bi_load, and remove any that
depend on calling bi_load first.

Reviewed by: imp, tsoome
Differential Revision: https://reviews.freebsd.org/D19374