x86/HVM: avoid effectively open-coding xzalloc_flex_struct()

Drop hvm_irq_size(), which exists for just this purpose.

There is a difference in generated code: xzalloc_bytes() forces
SMP_CACHE_BYTES alignment. I think we not only don't need this here, but
actually don't want it.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/hvm/hvm.c

@@ -642,7 +642,8 @@ int hvm_domain_initialise(struct domain *d)
     d->arch.hvm.params = xzalloc_array(uint64_t, HVM_NR_PARAMS);
     d->arch.hvm.io_handler = xzalloc_array(struct hvm_io_handler,
                                            NR_IO_HANDLERS);
-    d->arch.hvm.irq = xzalloc_bytes(hvm_irq_size(nr_gsis));
+    d->arch.hvm.irq = xzalloc_flex_struct(struct hvm_irq,
+                                          gsi_assert_count, nr_gsis);
 
     rc = -ENOMEM;
     if ( !d->arch.hvm.pl_time || !d->arch.hvm.irq ||

xen/include/asm-x86/hvm/irq.h

@@ -98,7 +98,6 @@ struct hvm_irq {
 #define hvm_pci_intx_link(dev, intx) \
     (((dev) + (intx)) & 3)
 #define hvm_domain_irq(d) ((d)->arch.hvm.irq)
-#define hvm_irq_size(cnt) offsetof(struct hvm_irq, gsi_assert_count[cnt])
 
 #define hvm_isa_irq_to_gsi(isa_irq) ((isa_irq) ? : 2)