move time64 socket options from arch bits to top-level sys/socket.h

now that all 32-bit archs have 64-bit time types, the values for the
time-related socket option macros can be treated as universal for
32-bit archs. the sys/socket.h mechanism for this predates
arch/generic and is instead in the top-level header.

x32, which does not use the new time64 values of the macros, already
has its own overrides, so this commit does not affect it.