xen/arm64: Correctly align VFP regs

On arm64, VFP instructions requires vfpregs to be 128-byte aligned.

By chance, the field is already correctly aligned. In the case if someone
decides to add a new field before, Xen will receive a data abort as soon as
it saves/restores VFP.

We are safe on arm32 as the only constraint is to be 32-byte aligned.

Reported-by: Chen Baozi <baozich@gmail.com>
Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

xen/include/asm-arm/arm64/vfp.h

@@ -1,9 +1,12 @@
 #ifndef _ARM_ARM64_VFP_H
 #define _ARM_ARM64_VFP_H
 
+/* ARM64 VFP instruction requires fpregs address to be 128-byte aligned */
+#define __vfp_aligned __attribute__((aligned(16)))
+
 struct vfp_state
 {
-    uint64_t fpregs[64];
+    uint64_t fpregs[64] __vfp_aligned;
     uint32_t fpcr;
     uint32_t fpexc32_el2;
     uint32_t fpsr;