phy: dp83640: select CONFIG_CRC32

Without crc32, this driver fails to link:

arm-linux-gnueabi-ld: drivers/net/phy/dp83640.o: in function `match':
dp83640.c:(.text+0x476c): undefined reference to `crc32_le'

Fixes: 539e44d2 ("dp83640: Include hash in timestamp/packet matching")
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Acked-by: NRichard Cochran <richardcochran@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/ptp/Kconfig

@@ -64,6 +64,7 @@ config DP83640_PHY
 	depends on NETWORK_PHY_TIMESTAMPING
 	depends on PHYLIB
 	depends on PTP_1588_CLOCK
+	select CRC32
 	help
 	  Supports the DP83640 PHYTER with IEEE 1588 features.