stm32: Integrate optional network.PPP.

Can be enabled by a board by enabling `MICROPY_PY_NETWORK_PPP_LWIP`.
Signed-off-by: Damien George <damien@micropython.org>

ports/stm32/lwip_inc/lwipopts.h

 #ifndef MICROPY_INCLUDED_STM32_LWIP_LWIPOPTS_H
 #define MICROPY_INCLUDED_STM32_LWIP_LWIPOPTS_H
 
-#include <stdint.h>
+#include "py/mpconfig.h"
 
 // This protection is not needed, instead we execute all lwIP code at PendSV priority
 #define SYS_ARCH_DECL_PROTECT(lev) do { } while (0)
@@ -36,6 +36,12 @@
 #define LWIP_MDNS_RESPONDER             1
 #define LWIP_IGMP                       1
 
+#if MICROPY_PY_LWIP_PPP
+#define PPP_SUPPORT                     1
+#define PAP_SUPPORT                     1
+#define CHAP_SUPPORT                    1
+#endif
+
 #define LWIP_NUM_NETIF_CLIENT_DATA      LWIP_MDNS_RESPONDER
 #define MEMP_NUM_UDP_PCB                (4 + LWIP_MDNS_RESPONDER)
 #define MEMP_NUM_SYS_TIMEOUT            (LWIP_NUM_SYS_TIMEOUT_INTERNAL + LWIP_MDNS_RESPONDER)
@@ -77,4 +83,7 @@ extern uint32_t rng_get(void);
 
 typedef uint32_t sys_prot_t;
 
+// Needed for PPP.
+#define sys_jiffies sys_now
+
 #endif // MICROPY_INCLUDED_STM32_LWIP_LWIPOPTS_H

ports/stm32/mpconfigport.h

@@ -106,6 +106,7 @@
 #define MICROPY_PY_TIME_GMTIME_LOCALTIME_MKTIME (1)
 #define MICROPY_PY_TIME_TIME_TIME_NS (1)
 #define MICROPY_PY_TIME_INCLUDEFILE "ports/stm32/modtime.c"
+#define MICROPY_PY_LWIP_PPP         (MICROPY_PY_NETWORK_PPP_LWIP)
 #define MICROPY_PY_LWIP_SOCK_RAW    (MICROPY_PY_LWIP)
 #ifndef MICROPY_PY_MACHINE
 #define MICROPY_PY_MACHINE          (1)