selftest/kho: update generation of initrd

selftest/kho: update generation of initrd

Use nolibc include directory rather than include a cumulative nolibc.h on
the compiler command line and replace use of 'sudo cpio' with
usr/gen_init_cpio.

While on it fix spelling of KHO_FINALIZE

Link: https://lkml.kernel.org/r/20250811082510.4154080-4-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Suggested-by: Thomas Weißschuh <linux@weissschuh.net>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>