selftest/arm64: Fix sve2p1_sigill() to hwcap test

selftest/arm64: Fix sve2p1_sigill() to hwcap test

The FEAT_SVE2p1 is indicated by ID_AA64ZFR0_EL1.SVEver. However,
the BFADD requires the FEAT_SVE_B16B16, which is indicated by
ID_AA64ZFR0_EL1.B16B16. This could cause the test to incorrectly
fail on a CPU that supports FEAT_SVE2.1 but not FEAT_SVE_B16B16.

LD1Q Gather load quadwords which is decoded from SVE encodings and
implied by FEAT_SVE2p1.

Fixes: c5195b027d29 ("kselftest/arm64: Add SVE 2.1 to hwcap test")
Signed-off-by: Yifan Wu <wuyifan50@huawei.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>