Move size optimization option outside of EMBEDDED menu, mark it EXPERIMENTAL

Also, disable on sparc64 - a number of people report breakage.  Probably
a compiler bug, but it's quite possible that it tickles some latent
kernel problem too.

It still defaults to 'y' everywhere else (when enabled through
EXPERIMENTAL), and Dave Jones points out that Fedora (and RHEL4) has
been building with size optimizations for a long time on x86, x86-64,
ia64, s390, s390x, ppc32 and ppc64.  So it is really only moderately
experimental, but the sparc64 breakage certainly shows that it can
trigger "issues".

Signed-off-by: Linus Torvalds <torvalds@osdl.org>