PPC: Get the correct cache line size from the AUXV

Hi.  The cache line size for PPC is currently hard-coded at 128 bytes.  I'm on a PA6T system, with 64 byte cache lines, so that doesn't work out at all...  (A large amount of tests fail randomly when making check)

This patch finds the smallest non-zero cache line size specified in the AUXV and uses that instead of 128 whenever possible.  With it applied, I get less than 0.5% fails from make ppc.release.check, so an immense improvement.  :-)