net: mdio: realtek-rtl9300: Add register structure

net: mdio: realtek-rtl9300: Add register structure

The MDIO controller of the Realtek Otto switches has either 4 or 7 command
registers. This depends on the number of supported ports. These registers
are "scattered" around the MMIO block and their addresses depend on the
specific model.

Nevertheless all command registers share a common pattern:

- A mask register with one bit per addressed port
  (remark: the driver internally works on ports instead of bus/address)
- A I/O data register that transfers the to be read/written data
- A C45 registers that takes devnum and regnum
- A C22 register that also includes run and status bits
  (remark: this also takes the Realtek proprietary C22 PHY page)

Provide an additional structure for these command registers so it can be
reused in two places.

1. For defining the register addresses in the regmap.
2. For defining the to be read/written register data

This will finally result in access patterns like

static int otto_emdio_run_cmd(u32 cmd,
                              struct rtl_mdio_cmd_regs *cmd_regs, ...)
{
  regmap_write(regmap, priv->info->reg->cmd_regs.c45_data,
                       cmd_regs->c45_data);
  ...
}

static int otto_emdio_9300_write_c45(...)
{
  struct otto_emdio_cmd_regs cmd_regs = {
    .c45_data  = ...
    .io_data   = ...,
    .port_mask = ...,
  };

  return otto_emdio_run_cmd(RTL9300_CMD_WRITE_C45, &cmd_regs, ...);
}

As a first step start with the C45 register. This one takes the
devnum/regnum data that is stored in the high/low 16 bits.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://patch.msgid.link/20260521175918.1494797-6-markus.stockhausen@gmx.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>