arm64: Relax GIC version check during early boot

Updates to the GIC architecture allow ID_AA64PFR0_EL1.GIC to have
values other than 0 or 1. At the moment, Linux is quite strict in the
way it handles this field at early boot stage (cpufeature is fine) and
will refuse to use the system register CPU interface if it doesn't
find the value 1.

Fixes: 021f653 ("irqchip: gic-v3: Initial support for GICv3")
Reported-by: Chase Conklin <Chase.Conklin@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/head.S

@@ -539,8 +539,7 @@ set_hcr:
 	/* GICv3 system register access */
 	mrs	x0, id_aa64pfr0_el1
 	ubfx	x0, x0, #24, #4
-	cmp	x0, #1
-	b.ne	3f
+	cbz	x0, 3f
 
 	mrs_s	x0, SYS_ICC_SRE_EL2
 	orr	x0, x0, #ICC_SRE_EL2_SRE	// Set ICC_SRE_EL2.SRE==1