net: ixp46x: fix ptp build failure

The rework of the ixp46x cpu detection left the network driver in
a half broken state:

drivers/net/ethernet/xscale/ptp_ixp46x.c: In function 'ptp_ixp_init':
drivers/net/ethernet/xscale/ptp_ixp46x.c:290:51: error: 'IXP4XX_TIMESYNC_BASE_VIRT' undeclared (first use in this function)
  290 |                 (struct ixp46x_ts_regs __iomem *) IXP4XX_TIMESYNC_BASE_VIRT;
      |                                                   ^~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/xscale/ptp_ixp46x.c:290:51: note: each undeclared identifier is reported only once for each function it appears in
drivers/net/ethernet/xscale/ptp_ixp46x.c: At top level:
drivers/net/ethernet/xscale/ptp_ixp46x.c:323:1: error: data definition has no type or storage class [-Werror]
  323 | module_init(ptp_ixp_init);

I have patches to complete the transition for a future release, but
for the moment, add the missing include statements to get it to build
again.

Fixes: 09aa9aab

 ("soc: ixp4xx: move cpu detection to linux/soc/ixp4xx/cpu.h")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>