Make second argument of gettimeofday as 'void *'

Also make the public prototype of gettimeofday declare its second
argument with type "void *" unconditionally, consistent with POSIX.

It is also consistent with POSIX.

Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64le-linux-gnu,
powerpc64-linux-gnu, powerpc-linux-gnu, and aarch64-linux-gnu.

Co-authored-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Lukasz Majewski <lukma@denx.de>