x86/hvm: increase struct hvm_vcpu_io's mmio_large_read[]

Since the emulator now supports a few 256-bit memory operations, this
array needs to follow (and the comments should, too).

To limit growth, re-order the mmio_large_write_* fields so that the
two mmio_large_*_bytes fields end up adjacent to each other.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/include/asm-x86/hvm/vcpu.h
+++ b/xen/include/asm-x86/hvm/vcpu.h
@@ -59,13 +59,13 @@ struct hvm_vcpu_io {
     unsigned long       mmio_gva;
     unsigned long       mmio_gpfn;
 
-    /* We may read up to m128 as a number of device-model transactions. */
+    /* We may read up to m256 as a number of device-model transactions. */
     paddr_t mmio_large_read_pa;
-    uint8_t mmio_large_read[16];
+    uint8_t mmio_large_read[32];
     unsigned int mmio_large_read_bytes;
-    /* We may write up to m128 as a number of device-model transactions. */
-    paddr_t mmio_large_write_pa;
+    /* We may write up to m256 as a number of device-model transactions. */
     unsigned int mmio_large_write_bytes;
+    paddr_t mmio_large_write_pa;
 };
 
 #define VMCX_EADDR    (~0ULL)