libpayload: Cache physical location of serial-console struct

In the presence of self-relocating payloads, it's safer to keep
physical addresses in `libsysinfo`.

Change-Id: Icd30e95c6b8115d16dd793914fb01a1a9da1854f
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43577
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>

payloads/libpayload/drivers/serial/ipq40xx.c

@@ -553,9 +553,7 @@ static struct console_output_driver consout = {};
 /* For simplicity's sake, let's rely on coreboot initializing the UART. */
 void serial_console_init(void)
 {
-	struct cb_serial *sc_ptr = lib_sysinfo.serial;
-
-	if (!sc_ptr)
+	if (!lib_sysinfo.cb_serial)
 		return;
 
 	consin.havekey = serial_havechar;