alpha: build fixes

This fixes some of the alpha-specific build problems, except a) modpost
warning about COMMON symbol "saved_config" and b) nasty final link
failure with gcc-4.x, -Os and scsi-disk driver configured built-in
(due to jump table in .rodata referencing discarded .exit.text).

- build failure with gcc-4.2.x: fix up casts in cia_io* routines to avoid
  warnings ('discards qualifiers from pointer target type'), which are
  failures, thanks to -Werror;
- modpost warnings: add missing __init qualifier for titan and marvel;
  for non-generic build, move machine vectors from .data to .data.init.refok
  section;
- unbreak CPU-specific optimization: rearrange cpuflags-y assignments
  so that extended -mcpu value (ev56, pca56, ev67) overrides basic
  one (ev5, ev6) and not vice versa.

Signed-off-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>