tcg/arm: Fix memory barrier encoding

I found with qemu 2.11.x or newer that I would get an illegal instruction
error running some Intel binaries on my ARM chromebook.  On investigation,
I found it was quitting on memory barriers.

qemu instruction:
mb $0x31
was translating as:
0x604050cc:  5bf07ff5  blpl     #0x600250a8

After patch it gives:
0x604050cc:  f57ff05b  dmb      ish

In short, I found INSN_DMB_ISH (memory barrier for ARMv7) appeared to be
correct based on online docs, but due to some endian-related shenanigans it
had to be byte-swapped to suit qemu; it appears INSN_DMB_MCR (memory
barrier for ARMv6) also should be byte swapped  (and this patch does so).
I have not checked for correctness of aarch64's barrier instruction.

Cc: qemu-stable@nongnu.org
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NHenry Wertz <hwertz10@gmail.com>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>
(cherry picked from commit 3f814b80)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

tcg/arm/tcg-target.inc.c

@@ -159,8 +159,8 @@ typedef enum {
     INSN_STRD_IMM  = 0x004000f0,
     INSN_STRD_REG  = 0x000000f0,
 
-    INSN_DMB_ISH   = 0x5bf07ff5,
-    INSN_DMB_MCR   = 0xba0f07ee,
+    INSN_DMB_ISH   = 0xf57ff05b,
+    INSN_DMB_MCR   = 0xee070fba,
 
     /* Architected nop introduced in v6k.  */
     /* ??? This is an MSR (imm) 0,0,0 insn.  Anyone know if this