x86/earlyprintk: Add a force option for pciserial device

x86/earlyprintk: Add a force option for pciserial device

The "pciserial" earlyprintk variant helps much on many modern x86
platforms, but unfortunately there are still some platforms with PCI
UART devices which have the wrong PCI class code. In that case, the
current class code check does not allow for them to be used for logging.

Add a sub-option "force" which overrides the class code check and thus
the use of such device can be enforced.

 [ bp: massage formulations. ]

Suggested-by: Borislav Petkov <[email protected]>
Signed-off-by: Feng Tang <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: "Stuart R . Anderson" <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Feng Tang <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: H Peter Anvin <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Kai-Heng Feng <[email protected]>
Cc: Kate Stewart <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Philippe Ombredanne <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Thymo van Beers <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]