phy: miphy365x: Pass sysconfig register offsets via syscfg dt property.

Based on Arnds review comments here https://lkml.org/lkml/2014/11/13/161

,
update the miphy365 phy driver to access sysconfig register offsets via
syscfg dt property.

This is because the reg property should not be mixing address spaces
like it does currently for miphy365. This change then also aligns us
to how other platforms such as keystone and bcm7445 pass there syscon
offsets via DT.

This patch breaks DT compatibility, but this platform is considered WIP,
and is only used by a few developers who are upstreaming support for it.
This change has been done as a single atomic commit to ensure it is
bisectable.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Tested-by: Maxime Coquelin <maxime.coquelin@st.com>