Revert "[PATCH] LOG2: Alter get_order() so that it can make use of ilog2() on a constant"

This reverts commit 39d61db0.

The commit was buggy in multiple ways:
 - the conversion to ilog2() was incorrect to begin with
 - it tested the wrong #defines, so on all architectures but FRV you'd
   never see the bug except for constant arguments.
 - the new "get_order()" macro used its arguments multiple times, and
   didn't even parenthesize them properly
 - despite the comments, it was not true that you could use it for
   constant initializers, since not all architectures even use the
   generic page.h header file.

All of the problems are individually fixable, but it all boils down to:
better just revert it, and re-do it from scratch.

Cc: David Howells <dhowells@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Andrew Morton <akpm@osdl.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>