KVM: arm64: expose SMCCC_ARCH_WORKAROUND_4 to guests

Wire up KVM support so that guests can detect the presence of
SMCCC_ARCH_WORKAROUND_4 and determine whether firmware has mitigated
CVE-2024-7881.

SMCCC_ARCH_WORKAROUND_4 is documented in the SMCCC 1.6 G BET0
specification, which can be found at:

  https://developer.arm.com/documentation/den0028/gbet0/?lang=en



Note that SMCCC_ARCH_WORKAROUND_4 has no return value, and exists solely
such that it can be detected via SMCCC_ARCH_FEATURES.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zenghui Yu <yuzenghui@huawei.com>
Cc: kvmarm@lists.linux.dev
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250128155428.210645-5-mark.rutland@arm.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>