ssb: sprom: add dev_id field for value overriding standard ID

Some devices may have different features despite sharing the same ID
(e.g. PCI ID). For example 14e4:4331 is usually a dual band, but this
can be "limited". Device with "pci/x/y/devid=0x4332" supports 2.4 GHz
only. Similarly 0x4333 will mean support for 5 GHz only.
Add entry in SPROM so info described above can be extracted and stored.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>