net: tsec: Use priv->tbiaddr to initialize TBI PHY address

Add a new member 'tbiaddr' to tsec_private struct. For non-DM driver,
it is initialized as CONFIG_SYS_TBIPA_VALUE, but for DM driver, we
can get this from device tree. Update the bindings doc as well.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

include/tsec.h

@@ -402,6 +402,7 @@ struct tsec_private {
 	phy_interface_t interface;
 	struct mii_dev *bus;
 	uint phyaddr;
+	uint tbiaddr;
 	char mii_devname[16];
 	u32 flags;
 	uint rx_idx;	/* index of the current RX buffer */