arm64: hyp: initialize vttbr_el2 to zero

The architecture doesn't mandate any reset value for vttbr_el2.
Better set it to a known value before some HYP code gets confused.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/head.S

@@ -185,6 +185,9 @@ ENTRY(el2_setup)
 	msr	hstr_el2, xzr			// Disable CP15 traps to EL2
 #endif
 
+	/* Stage-2 translation */
+	msr	vttbr_el2, xzr
+
 	/* Hypervisor stub */
 	adr	x0, __hyp_stub_vectors
 	msr	vbar_el2, x0