rv: Support systems with time64-only syscalls

rv: Support systems with time64-only syscalls

Some systems (like 32-bit RISC-V) only have the 64-bit time_t versions
of syscalls.  So handle the 32-bit time_t version of those being
undefined.

Fixes: f74f8bb246cf ("rv: Add rtapp_sleep monitor")
Closes: https://lore.kernel.org/oe-kbuild-all/202508160204.SsFyNfo6-lkp@intel.com
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
Acked-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/r/20250804194518.97620-2-palmer@dabbelt.com
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>