NetsecDxe: embed phy address into NETSEC SDK internal structure

This is a refactoring of phy address handling in Netsec driver.
NETSEC SDK, low level driver for NetsecDxe, did not store phy address.
User should specify the phy address as an argument to
the SDK public functions.
It prevented NETSEC SDK from internally controlling phy,
and it also bothers user application with phy address management.

With that, we encapsulate the phy address into NETSEC SDK.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>