net: phy: smsc: LAN8740: add PHY_RST_AFTER_CLK_EN flag

The LAN8740, like the 8720, also requires a reset after enabling clock.
The datasheet [1] 3.8.5.1 says:
	"During a Hardware reset, an external clock must be supplied
	to the XTAL1/CLKIN signal."

I have observed this issue on a custom i.MX6 based board with
the LAN8740A.

[1] http://ww1.microchip.com/downloads/en/DeviceDoc/8740a.pdf



Signed-off-by: Martin Fuzzey <martin.fuzzey@flowbird.group>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>