update to new regz package layout

[Tiedye]

Not sure what to call this, but these are the changes I had to make to get this program to work:

const hal = @import("microzig").hal;
const micro = @import("microzig");

pub fn main() !void {
    const led = hal.parsePin(micro.board.pin_map.D13);
    const Port = hal.Uart(0, .{});
    var serial = try Port.init(.{
        .baud_rate = 115200,
        .parity = null,
        .stop_bits = .one,
        .data_bits = .eight,
    });
    hal.gpio.setOutput(led);
    hal.gpio.write(led, .low);
    while (true) {
        busyloop();
        hal.gpio.toggle(led);
        serial.tx('a');
    }
}

fn busyloop() void {
    const limit = 1_000_000;

    var i: u24 = 0;
    while (i < limit) : (i += 1) {
        asm volatile ("");
    }
}