phy: core: Add consumer device link support

In order to enforce suspend/resume ordering, this commit creates link
between phy consumers and phy devices. This link avoids to suspend phy
before phy consumers.

Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
[jonathanh@nvidia.com: Fix an abort when of_phy_get() returns error]
Signed-off-by: Jonathan Hunter <jonathanh@nvidia.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>