bootloader: improve launch code

- Fix error not showing if payload is missing or can't be read
- Move errors to their callee function to save binary space
- Refactor various parameters and comments
- Reduce size on some errors
- Do not read HOS specific config in case of payload launch
- Remove unneeded code

bootloader/hos/hos.c

@@ -1178,5 +1178,7 @@ int hos_launch(ini_sec_t *cfg)
 error:
 	emmc_end();
 
+	EPRINTF("\nFailed to launch HOS!");
+
 	return 0;
 }