[v2] Add MatchDMI support in InputClass sections

[Daniel Martin]

Hi *,

this is the second version of my patches to make it possible to match on
DMI identifiers from within an InputClass section to be able to work
around shortcomings we've to face with certain hardware (i.e. synaptics
touchpads).

v2:
- based on Keiths warning-fixes branch
- uses '|' as logical 'or' in MatchDMI lines and key-value pairs are
  separated by a ':'
- maps the sysfs entries nearly 1:1 to keys (except for sys_vendor ->
  system_vendor)

Cheers,
    Daniel Martin