selftests/powerpc/dexcr: Fix spelling mistake "predicition" -> "prediction"

There is a spelling mistake in the help message. Fix it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240508084117.2869261-1-colin.i.king@gmail.com

selftests/powerpc/dexcr: Add chdexcr utility

Adds a utility to exercise the prctl DEXCR inheritance in the shell.
Supports setting and clearing each aspect.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
[mpe: Use correct SPDX license, use execvp() for usability, print errors]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240417112325.728010-9-bgray@linux.ibm.com