hw/sd: Fix sun4i allwinner-sdhost for U-Boot

Trying to run U-Boot for Cubieboard (Allwinner A10) fails because it cannot
access SD card. The problem is that FIFO register in current
allwinner-sdhost implementation is at the address corresponding to
Allwinner H3, but not A10.
Linux kernel is not affected since Linux driver uses DMA access and does
not use FIFO register for reading/writing.

This patch adds new class parameter `is_sun4i` and based on that
parameter uses register at offset 0x100 either as FIFO register (if
sun4i) or as threshold register (if not sun4i; in this case register at
0x200 is FIFO register).

Tested with U-Boot and Linux kernel image built for Cubieboard and
OrangePi PC.

Signed-off-by: Strahinja Jankovic <strahinja.p.jankovic@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20221112214900.24152-1-strahinja.p.jankovic@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/hw/sd/allwinner-sdhost.h

@@ -130,6 +130,7 @@ struct AwSdHostClass {
 
     /** Maximum buffer size in bytes per DMA descriptor */
     size_t max_desc_size;
+    bool   is_sun4i;
 
 };