wifi: mt76: mt7996: add macros for pci device ids

wifi: mt76: mt7996: add macros for pci device ids

The chipset name (i.e., brand name) used by the driver may cause confusion
with the PCI device ID when adding support for new chipsets.

| Chipset name | PCI device id  |
|--------------|----------------|
| 7996         | 0x7990, 0x7991 |
| 7992         | 0x7992, 0x799a |
| 7990         | 0x7993, 0x799b |

To prevent confusion, replace the code that directly uses the device ID
with macros. This is a preliminary patch to support mt7990 chipset.

Co-developed-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Link: https://patch.msgid.link/20250409140750.724437-2-shayne.chen@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>