time: Add 64-bit time support for getdate

The getdate is basically a wrapper localtime and mktime.  The 64-bit
time support is done calling the 64-bit internal functions, there is
no need to add a new symbol version.

Checked on x86_64-linux-gnu and i686-linux-gnu.

Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>