KVM: arm64: vgic-v3: Don't advertise ICC_CTLR_EL1.SEIS

Since we are trapping all sysreg accesses when ICH_VTR_EL2.SEIS
is set, and that we never deliver an SError when emulating
any of the GICv3 sysregs, don't advertise ICC_CTLR_EL1.SEIS.

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211010150910.2911495-5-maz@kernel.org