thinkpad-acpi: store fw version with strict checking

Extend the thinkpad model and firmware identification data with the
release serial number for the BIOS and firmware (when available), as
that is easier to parse and compare than the version strings.

We're going to greatly extend the use of the ThinkPad DMI data through
quirk lists, so it is best to be quite strict and make sure what we
get from DMI is exactly what we expect, otherwise quirk matching may
result in quite insane things.

IBM (and Lenovo, at least for the ThinkPad line) uses this schema for
firmware versioning and model:

Firmware model: Two digits, [0-9A-Z]

Firmware version: AABBCCDD, where
  AA = firmware model, see above
  BB = "ET" for BIOS, "HT" for EC
  CC = release version, two digits, [0-9A-Z],
       "00" < "09" < "0A" < "10" < "A0" < "ZZ"
  DD = "WW"

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>