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/8250.c

@@ -132,9 +132,9 @@ void serial_init(void)
 
 void serial_console_init(void)
 {
-	if (!lib_sysinfo.serial)
+	if (!lib_sysinfo.cb_serial)
 		return;
-	cb_serial = *lib_sysinfo.serial;
+	cb_serial = *(struct cb_serial *)phys_to_virt(lib_sysinfo.cb_serial);
 
 	serial_init();