arm64: cpufeature: Export matrix and other features to userspace

Export the features introduced as part of ARMv8.6 exposed in the
ID_AA64ISAR1_EL1 and ID_AA64ZFR0_EL1 registers. This introduces the
Matrix features (ARMv8.2-I8MM, ARMv8.2-F64MM and ARMv8.2-F32MM) along
with BFloat16 (Armv8.2-BF16), speculation invalidation (SPECRES) and
Data Gathering Hint (ARMv8.0-DGH).

Signed-off-by: Julien Grall <julien.grall@arm.com>
[Added other features in those registers]
Signed-off-by: Steven Price <steven.price@arm.com>
[will: Don't advertise SPECRES to userspace]
Signed-off-by: Will Deacon <will@kernel.org>