MFC 200309:

MFC 200309:
- Port bios_getmem() from libi386 to {gpt,}zfsboot() and use it to
  safely allocate a heap region above 1MB.  This enables {gpt,}zfsboot()
  to allocate much larger buffers than before.
- Use a larger buffer (1MB instead of 128K) for temporary ZFS buffers.  This
  allows more reliable reading of compressed files in a raidz/raidz2 pool.

git-svn-id: svn://svn.freebsd.org/base/stable/8@200689 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f