realtek: convert access to RTL931x "digital 2" serdes pages

realtek: convert access to RTL931x "digital 2" serdes pages

The RTL931x has 14 frontend and at least 26 backend serdes. Currently
the programming functions always need to determine the right backend
serdes from the given frontend serdes on their own. We plan to provide
a consistent serdes mapping to all callers.

As the third step make use of these new functions whenever we want to
access the "digital 2" pages. The pages are mapped starting at 0x200.
So the function conversion is as simple as this:

Old:
dsds = (sds - 1) * 2;
rtmdio_931x_read_sds_phy(dsds + 1, page, ...)

New:
rtmdio_931x_read_sds_phy_new(sds, page + 0x200, ...)

Signed-off-by: Markus Stockhausen <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/19873
Signed-off-by: Hauke Mehrtens <[email protected]>