of: Fix kerneldoc output formatting

The indentation of the kerneldoc comments affects the output formatting.
Leading tabs in particular don't work, sections need to be indented
under the section header, and several code blocks are reformatted.

Cc: Frank Rowand <frowand.list@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/20210326192606.3702739-1-robh@kernel.org