Enable VDSO for static linking on mips

I have tested that this builds and the resulting program still work.

This was tested on gcc23.fsffrance.org, and for some reason the vdso
there seems unused even when using shared libraries.

	[BZ #19767]
	* sysdeps/unix/sysv/linux/mips/init-first.c: Remove #ifdef SHARED.
        * sysdeps/unix/sysv/linux/mips/libc-vdso.h: Remove #ifdef SHARED.
        * sysdeps/unix/sysv/linux/mips/mips32/sysdep.h: Define
	ALWAYS_USE_VSYSCALL.
        * sysdeps/unix/sysv/linux/mips/mips64/n32/sysdep.h: Define
	ALWAYS_USE_VSYSCALL.
	* sysdeps/unix/sysv/linux/mips/mips64/n64/sysdep.h: Define
	ALWAYS_USE_VSYSCALL.