selftests: arm64: Add test for the SVE ptrace interface

Add a test case that does some basic verification of the SVE ptrace
interface, forking off a child with known values in the registers and
then using ptrace to inspect and manipulate the SVE registers of the
child, including in FPSIMD mode to account for sharing between the SVE
and FPSIMD registers.

This program was written by Dave Martin and modified for kselftest by
me.

Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20200819114837.51466-3-broonie@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>