arm64/sme: Enable host kernel to access ZT0

The new register ZT0 introduced by SME2 comes with a new trap, disable it
for the host kernel so that we can implement support for it.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221208-arm64-sme2-v4-7-f2fa0aef982f@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>