WIP: Add support for RTL82328 dialect

[mrnuke]

THIS IS JUST A PROOF OF CONCEPT DO NOT NMERGE THIS!

This PR is for testing purposes only. Bu creating a PR, github should run a pipeline and create an installable package for others to test. That is the purpose of publishing a PR this early in development.

Add initial support for the PoE dialect used by RTL8238B PSE chips.

The original code separation assumed that there would be significant differences in the command structures. I designed the separation interface to be fairly high level, such as:

struct poe_dialect {
    int (*init_async)(const struct config *cfg);
    int (*init_ports_async)(const struct config *cfg);
    int (*enable_port_async)(uint8_t port, uint8_t enable);
    int (*poll_async)(const struct config *cfg);
    int (*handle_reply)(struct mcu_state *ctx, uint8_t *reply, size_t len);
};

Many commands are very similar between the the two dialects. The command IDs differ. The original split now menas tha a lot of code is duplicated. I am quite unhappy with the separation.

It is now clear that a better approach is to have common code implementing the dialects, and have a mapping bewteen command and command_id of the dialect.

enum poe_cmd {
    POE_CMD_NONE = 0,
    POE_CMD_SET_XYZ,
    ...
    POE_CMD_SET_XYZ,
    ...
};

poe_cmd_set_xyz(struct poe_dialect *dialect, ...)
{
    uint8_t cmd = dialect_map(dialect, POE_CMD_SET_XYZ);

    poe_cmd_queue(cmd, ...);
}

const struct dialect_map __map = {
    [POE_CMD_SET_XYZ] = { 0x42, CMD_4_PORT, CMD_ALL_PORT },
    ...
};

The flags may seem obscure. Most command dealing with a port number can take more than one (port, value) argument pair. For example 01 <val>02 <val> 03 <val> ff ff, up to four pairs per command, with ff meaning "nothing to see here. This is the use case for the 4port command function:

static int poet_cmd_4_port(uint8_t cmd_id, uint8_t port[4], uint8_t data[4])
{
    uint8_t cmd[] = { cmd_id, 0x00, port[0], data[0], port[1], data[1],
        port[2], data[2], port[3], data[3] };

        return poe_cmd_queue(cmd, sizeof(cmd));
}

Other commands can use 7f as the port ID to configure all ports with the same value: 7f <val>. The flags in dialect map would indicate which commands can use such optimizations.

I am hoping that restructuring the code in this manner would reduce duplication, and actually make a PR that makes some sense.