software/bios: move romboot after serialboot and netboot

On designs using romboot (firmware embedded in ram blocks), we generally upload new firmwares with serialboot and netboot for prototyping.
Moving romboot after serialboot and netboot avoid manual interrupts of the boot sequence.

misoc/software/bios/main.c

@@ -510,9 +510,6 @@ static void boot_sequence(void)
 	if(test_user_abort()) {
 #ifdef FLASH_BOOT_ADDRESS
 		flashboot();
-#endif
-#ifdef ROM_BOOT_ADDRESS
-		romboot();
 #endif
 		serialboot();
 #ifdef CSR_ETHMAC_BASE
@@ -520,6 +517,9 @@ static void boot_sequence(void)
 		eth_mode();
 #endif
 		netboot();
+#endif
+#ifdef ROM_BOOT_ADDRESS
+		romboot();
 #endif
 		printf("No boot medium found\n");
 	}