fel: Fix SPL size check against thunk addr

We have a check to avoid that the SPL accidentally overwrites the thunk
buffer we use to execute code on the board.

Unfortunately this compares the SPL *size* against the thunk *address*,
which is only valid when the SPL starts at 0 (older 32-bit SoCs).

Factor in the SoC dependent SPL start address, to make this check work
properly on newer (64-bit) SoCs.
Signed-off-by: Andre Przywara <osp@andrep.de>

fel.c

@@ -808,8 +808,8 @@ void aw_fel_write_and_execute_spl(feldev_handle *dev, uint8_t *buf, size_t len)
 	}
 
 	/* Clarify the SPL size limitations, and bail out if they are not met */
-	if (soc_info->thunk_addr < spl_len_limit)
-		spl_len_limit = soc_info->thunk_addr;
+	if (soc_info->thunk_addr - soc_info->spl_addr < spl_len_limit)
+		spl_len_limit = soc_info->thunk_addr - soc_info->spl_addr;
 
 	if (spl_len > spl_len_limit)
 		pr_fatal("SPL: too large (need %u, have %u)\n",