checkpatch: Handle continuation headers

Continuation headers baffle checkpatch, as it can only operate
on one line of context at a time.  When continuation headers are found,
put them up with the header they're continuing so the whole thing
can be parsed in a single line of context.

Change-Id: I2d22ed056f8203ae6dae473b01ae66bc1963ae75
Signed-off-by: Gregory Bean <gbean@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>