phy: Include NC-SI in phy setup

Add NC-SI to the usual phy handling. This makes two notable changes:
- Somewhat similar to a fixed phy, phy_connect() will create an NC-SI
phy if CONFIG_PHY_NCSI is defined.
- An early return is added to phy_read() and phy_write() to handle a
case like the NC-SI phy which does not define a bus.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

include/phy_interface.h

@@ -31,6 +31,7 @@ typedef enum {
 	PHY_INTERFACE_MODE_XLAUI,
 	PHY_INTERFACE_MODE_CAUI2,
 	PHY_INTERFACE_MODE_CAUI4,
+	PHY_INTERFACE_MODE_NCSI,
 	PHY_INTERFACE_MODE_XFI,
 	PHY_INTERFACE_MODE_USXGMII,
 	PHY_INTERFACE_MODE_NONE,	/* Must be last */
@@ -60,6 +61,7 @@ static const char * const phy_interface_strings[] = {
 	[PHY_INTERFACE_MODE_XLAUI]		= "xlaui4",
 	[PHY_INTERFACE_MODE_CAUI2]		= "caui2",
 	[PHY_INTERFACE_MODE_CAUI4]		= "caui4",
+	[PHY_INTERFACE_MODE_NCSI]		= "NC-SI",
 	[PHY_INTERFACE_MODE_XFI]		= "xfi",
 	[PHY_INTERFACE_MODE_USXGMII]		= "usxgmii",
 	[PHY_INTERFACE_MODE_NONE]		= "",