kselftest/arm64: Parameterise ptrace vector length information

SME introduces a new mode called streaming mode in which the SVE registers
have a different vector length. Since the ptrace interface for this is
based on the existing SVE interface prepare for supporting this by moving
the regset specific configuration into  struct and passing that around,
allowing these tests to be reused for streaming mode. As we will also have
to verify the interoperation of the SVE and streaming SVE regsets don't
just iterate over an array.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20211210184133.320748-5-broonie@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>