Documentation: driver-api: correct spelling

Correct spelling problems for Documentation/driver-api/ as reported
by codespell.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: nvdimm@lists.linux.dev
Cc: Vinod Koul <vkoul@kernel.org>
Cc: dmaengine@vger.kernel.org
Cc: linux-raid@vger.kernel.org
Cc: linux-usb@vger.kernel.org
Acked-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230129231053.20863-3-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: split up serial-interfaces.rst

It never made sense to keep these documents together; move each into its
own file.

Drop the section numbering on hsi.txt on its way to its own file.

Suggested-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>