Ported over the more efficient linux crc32() function.
A quick comparsion on ppc:
After changing the old crc32 to do 4 bytes in the
inner loop to be able to compare with new version one can note:
- old inner loop has 61 insn, new has 19 insn.
- new crc32 does one 32 bit load of data to crc while
  the old does four 8 bits loads.
- size is bit bigger for the new crc32:
  1392(old) 1416(new) of text. The is because the new version
  shares code with crc32_no_comp() instead of duplicating code.
- about 33% faster on ppc:
  New > crc 0 0xfffffff -> 39 secs
  Old > crc 0 0xfffffff -> 60 secs

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>