x86: shrink __ALIGN and __ALIGN_STR definitions

Impact: cleanup

1) .p2align 4 and .align 16 are the same meaning
   (until a.out format for i386 is used which is
    not our case for CONFIG_X86_ALIGNMENT_16 anyway)

2) having 15 as max allowed bytes to be skipped
   does not make sense on modulo 16

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
LKML-Reference: <20090309171951.GE9945@localhost>
[ small cleanup, use __stringify(), etc. ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>