uImage: increase the gzip load size

Recent u-boot has different defines for its gzip extract buffer, but the
common ground seems to be 64MB. So let's bump it up to that, enabling me
to load my test image again ;).

Signed-off-by: Alexander Graf <agraf@suse.de>

hw/loader.c

@@ -377,9 +377,9 @@ static void zfree(void *x, void *addr)
 
 #define DEFLATED	8
 
-/* This is the maximum in uboot, so if a uImage overflows this, it would
+/* This is the usual maximum in uboot, so if a uImage overflows this, it would
  * overflow on real hardware too. */
-#define UBOOT_MAX_GUNZIP_BYTES 0x800000
+#define UBOOT_MAX_GUNZIP_BYTES (64 << 20)
 
 static ssize_t gunzip(void *dst, size_t dstlen, uint8_t *src,
                       size_t srclen)