checkpatch: check compatible strings in .c and .h too

Look for ".compatible = "foo" strings not only in .dts files, but
in .c and .h too.

Change-Id: I31583ed439e68e9ac278539df290758beea5cca6
Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
Cc: Joe Perches <joe@perches.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 7dd05b38e5b729f412b617baad5c3363519cf1d4
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>