kexec: fix for the x32 ABI

kexec: fix for the x32 ABI

There is no compat (and no 32-bit version, ever) for x32 ABI, so
kernel's long type should be used for arguments' values.

The only remaining thing is a pointer to cmdline string, but it is
currently broken on x32 anyway.

* kexec.c (SYS_FUNC(kexec_file_load)): Print the cmdline_len argument
as kernel long, retrieve it via getarg_klu; use printflags64 for
printing the flags argument, retrieve it via getarg_klu.