x32, mips n32: make printargs print full 64-bit syscall arguments

x32, mips n32: make printargs print full 64-bit syscall arguments

As most of x32 syscalls are regular x86_64 syscalls, they should be
printed by default as 64-bit syscalls, and syscall parsers at their
discretion might print syscalls differently.  This is already
implemented in 64-bit strace tracing x32 personality processes,
and now x32 strace will also behave this way.

Similar reasoning applies to mips n32.

* util.c (printargs) [HAVE_STRUCT_TCB_EXT_ARG]: Print syscall arguments
from ext_arg array using %llx format.