x86/vdso2c: Use better macros for ELF bitness

Rather than using a separate macro for each replacement, use generic
macros.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/d953cd2e70ceee1400985d091188cdd65fba2f05.1403129369.git.luto@amacapital.net


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>