selftests: arm64: Use a define for the number of SVE ptrace tests to be run

Partly in preparation for future refactoring move from hard coding the
number of tests in main() to putting #define at the top of the source
instead.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210913125505.52619-2-broonie@kernel.org


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