Duplicate vsyscall/vdso gettimeofday implementations on x86_64

[john stultz <johnstul@us.ibm.com>]

Hey Andi, Ingo, Thomas,
	I ran across an oddity recently in the x86_64 vsyscall code.
Specifically I was looking at the vsyscall clock_gettime()
implementation in arch/x86/vdso/vclock_gettime.c, and noticed there is a
vsyscall gettimeofday implementation there too! This seems to duplicate
the do_vgettimeofday implementation in arch/x86/kernel/vsyscall_64.c

I think the implementation in vclock_gettime.c is nice, as it mostly
reuses the clock_gettime() code, but I don't think it actually gets
called.

I'm a little worried about just switching it out, and cleaning it up, as
I don't know enough yet about how the vgettimeofday is called from glibc
(I thought it was a static "jump to this page and run" mapping).

Andi: You wrote the vclock_gettime.c, do you have any pointers about
where you were going with this? Is there a reason you didn't clean it up
when you implemented it originally?

thanks
-john