Change FIFO size to 4KB (not sure)

The datasheet says 2KB FIFO, but accroding to many
code examples, the F1C100s has at least 4KB of FIFO memory.
This is working with cdc_msc example,
but I'm not sure, this should be checked.

src/portable/sunxi/dcd_sunxi_musb.c

@@ -389,7 +389,7 @@ static inline void print_block_list(free_block_t const *blk, unsigned num)
 #endif
 
 #if CFG_TUSB_MCU == OPT_MCU_F1C100S
-#define USB_FIFO_SIZE_KB 2
+#define USB_FIFO_SIZE_KB 4
 #else
 #error "Unsupported MCU"
 #endif