memory: inline and optimize devend_memop

devend_memop can rely on the fact that the result is always either
0 or MO_BSWAP, corresponding respectively to host endianness and
the opposite.  Native (target) endianness in turn can be either
the host endianness, in which case MO_BSWAP is only returned for
host-opposite endianness, or the opposite, in which case 0 is only
returned for host endianness.

With this in mind, devend_memop can be compiled as a setcond+shift
for every target.  Do this and, while at it, move it to
include/exec/memory.h since !NEED_CPU_H files do not (and should not)
need it.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

memory.c

@@ -3267,21 +3267,3 @@ static void memory_register_types(void)
 }
 
 type_init(memory_register_types)
-
-MemOp devend_memop(enum device_endian end)
-{
-    static MemOp conv[] = {
-        [DEVICE_LITTLE_ENDIAN] = MO_LE,
-        [DEVICE_BIG_ENDIAN] = MO_BE,
-        [DEVICE_NATIVE_ENDIAN] = MO_TE,
-        [DEVICE_HOST_ENDIAN] = 0,
-    };
-    switch (end) {
-    case DEVICE_LITTLE_ENDIAN:
-    case DEVICE_BIG_ENDIAN:
-    case DEVICE_NATIVE_ENDIAN:
-        return conv[end];
-    default:
-        g_assert_not_reached();
-    }
-}