Always use an allocated buffer for {Read,Write}Blocks() to make

Always use an allocated buffer for {Read,Write}Blocks() to make
efid_io() simpler.  Also fixes the problem on some machines when boot
from CD-ROM.  It happened because the previous version passed
unaligned pointers to the functions even if it is restricted by the
IoAlign property of the media.  idea from kettenis, work with asou

ok kettenis