irqchip/gic-v4.1: Disable vSGI upon (GIC CPUIF < v4.1) detection

GIC CPU interfaces versions predating GIC v4.1 were not built to
accommodate vINTID within the vSGI range; as reported in the GIC
specifications (8.2 "Changes to the CPU interface"), it is
CONSTRAINED UNPREDICTABLE to deliver a vSGI to a PE with
ID_AA64PFR0_EL1.GIC < b0011.

Check the GIC CPUIF version by reading the SYS_ID_AA64_PFR0_EL1.

Disable vSGIs if a CPUIF version < 4.1 is detected to prevent using
vSGIs on systems where they may misbehave.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210317100719.3331-2-lorenzo.pieralisi@arm.com