goldfish_rtc: Add big-endian property

Add a new property "big-endian" to allow configuring the RTC as either
little or big endian, the default is little endian.

Currently overriding the default to big endian is only used by the m68k
virt platform.  New platforms should prefer to use little endian and not
set this.

Cc: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Stafford Horne <shorne@gmail.com>

include/hw/rtc/goldfish_rtc.h

@@ -42,6 +42,8 @@ struct GoldfishRTCState {
     uint32_t irq_pending;
     uint32_t irq_enabled;
     uint32_t time_high;
+
+    bool big_endian;
 };
 
 #endif