xen/dom0less: abstract Arm-specific p2m type name for device MMIO mappings

Introduce arch_dt_passthrough_p2m_type() and use it instead of
`p2m_mmio_direct_dev` to avoid leaking Arm-specific naming into
common Xen code, such as dom0less passthrough property handling.

This helps reduce platform-specific terminology in shared logic and
improves clarity for future non-Arm ports (e.g. RISC-V or PowerPC).

No functional changes — the definition is preserved via a static inline
function for Arm.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>

xen/arch/arm/include/asm/p2m.h

@@ -137,6 +137,11 @@ typedef enum {
     p2m_max_real_type,  /* Types after this won't be store in the p2m */
 } p2m_type_t;
 
+static inline p2m_type_t arch_dt_passthrough_p2m_type(void)
+{
+    return p2m_mmio_direct_dev;
+}
+
 /* We use bitmaps and mask to handle groups of types */
 #define p2m_to_mask(_t) (1UL << (_t))
 

xen/common/device-tree/dom0less-build.c

@@ -185,7 +185,7 @@ static int __init handle_passthrough_prop(struct kernel_info *kinfo,
                                gaddr_to_gfn(gstart),
                                PFN_DOWN(size),
                                maddr_to_mfn(mstart),
-                               p2m_mmio_direct_dev);
+                               arch_dt_passthrough_p2m_type());
         if ( res < 0 )
         {
             printk(XENLOG_ERR