net: pcs: rzn1-miic: Move configuration data to SoC-specific struct

net: pcs: rzn1-miic: Move configuration data to SoC-specific struct

Move configuration data such as the modctrl matching table, converter
count, and string lookup tables into the SoC-specific miic_of_data
structure. Update the helper functions to use the per-SoC configuration
instead of relying on fixed-size arrays or global tables, and allocate
DT configuration memory dynamically.

This refactoring keeps the existing RZ/N1 support intact while preparing
the driver to handle the different configuration requirements of the
RZ/T2H SoC.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://patch.msgid.link/20250910204132.319975-5-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>