alpha: cleanup in bitops.h

Remove 2 functions private to the alpha implemetation,
in favor of similar functions in <linux/log2.h>.

Provide a more efficient version of the fls64 function
for pre-ev67 alphas.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>