fix: support fan p5c fan-level

[tiancheng91]

support fan dmaker.fan.p5c with stepless speed control.

[tiancheng91]

功能正常，但显示有点奇怪，fan-level变成独立实体了(滑条那个)，修改前是个正常的fan控件

[SusanPhevos]

SPEC_SERVICE_TRANS_MAP in xiaomi_home/miot/specs/specv2entity.py defines how a MIoT-Spec-V2 fan service can be converted to a Home Assistant fan entity. See here. A "on" property and a "fan-level" property are required in a fan service. If there is no "on" property, the fan service will not be converted to a fan entity.
Futhermore, in Mi Home APP, the stepless fan-level setting entry is only shown when the fan mode is "Straight Wind". When the fan mode is "Natural Wind", the fan-level has four level options. There is no need to support the stepless fan-level in the fan entity.

[tiancheng91]

todo : adapt to mode selection, use different properties as the percent value for different modes. For the natural wind mode, use the fan-level property with a value-list, and for the direct wind mode, use the speed-level property with a value-range

[tiancheng91]

SPEC_SERVICE_TRANS_MAP in xiaomi_home/miot/specs/specv2entity.py defines how a MIoT-Spec-V2 fan service can be converted to a Home Assistant fan entity. See here. A "on" property and a "fan-level" property are required in a fan service. If there is no "on" property, the fan service will not be converted to a fan entity. Futhermore, in Mi Home APP, the stepless fan-level setting entry is only shown when the fan mode is "Straight Wind". When the fan mode is "Natural Wind", the fan-level has four level options. There is no need to support the stepless fan-level in the fan entity.

Great, I understand. I'll close this MR first, and I'll try to adapt mode when I have time later.