memory: Introduce DEVICE_HOST_ENDIAN for ram device

At the moment ram device's memory regions are DEVICE_NATIVE_ENDIAN. It's
incorrect. This memory region is backed by a MMIO area in host, so the
uint64_t data that MemoryRegionOps read from/write to this area should be
host-endian rather than target-endian. Hence, current code does not work
when target and host endianness are different which is the most common case
on PPC64. To fix it, this introduces DEVICE_HOST_ENDIAN for the ram device.

This has been tested on PPC64 BE/LE host/guest in all possible combinations
including TCG.

Backports commit c99a29e702528698c0ce2590f06ca7ff239f7c39 from qemu

qemu/include/exec/cpu-common.h

@@ -22,6 +22,12 @@ enum device_endian {
     DEVICE_LITTLE_ENDIAN,
 };
 
+#if defined(HOST_WORDS_BIGENDIAN)
+#define DEVICE_HOST_ENDIAN DEVICE_BIG_ENDIAN
+#else
+#define DEVICE_HOST_ENDIAN DEVICE_LITTLE_ENDIAN
+#endif
+
 /* address in the RAM (different from a physical address) */
 #if defined(CONFIG_XEN_BACKEND)
 typedef uint64_t ram_addr_t;

qemu/memory.c

@@ -1064,7 +1064,7 @@ static const MemoryRegionOps ram_device_mem_ops = {
     memory_region_ram_device_write,
     NULL,
     NULL,
-    DEVICE_NATIVE_ENDIAN,
+    DEVICE_HOST_ENDIAN,
     // valid
     {
         1, 8,