xen/arm: Fix build issue when CONFIG_PHYS_ADDR_T_32=y

On Arm32, when CONFIG_PHYS_ADDR_T_32 is set, a build failure is observed:
arch/arm/platforms/vexpress.c: In function 'vexpress_smp_init':
arch/arm/platforms/vexpress.c:102:12: error: format '%lx' expects argument of type 'long unsigned int', but argument 2 has type 'long long unsigned int' [-Werror=format=]
  102 |     printk("Set SYS_FLAGS to %"PRIpaddr" (%p)\n",

When CONFIG_PHYS_ADDR_T_32 is set, paddr_t is defined as unsigned long.
Commit 96f35de69e dropped __virt_to_maddr() which used paddr_t as a
return type. Without a cast, the expression type is unsigned long long
which causes the issue. Fix it.

Fixes: 96f35de69e ("x86+Arm: drop (rename) __virt_to_maddr() / __maddr_to_virt()")
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Tested-by: Luca Fancellu <luca.fancellu@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/include/asm/mm.h

@@ -263,7 +263,7 @@ static inline void __iomem *ioremap_wc(paddr_t start, size_t len)
 
 #define virt_to_maddr(va) ({                                        \
     vaddr_t va_ = (vaddr_t)(va);                                    \
-    (va_to_par(va_) & PADDR_MASK & PAGE_MASK) | (va_ & ~PAGE_MASK); \
+    (paddr_t)((va_to_par(va_) & PADDR_MASK & PAGE_MASK) | (va_ & ~PAGE_MASK)); \
 })
 
 #ifdef CONFIG_ARM_32