media: hist-v4l2.rst: remove :c:`type` from structs and enums

Using struct|enum :c:`type` here sounds a bad idea, as it may be
documenting data types that were already removed. Also, it makes
the file harder to read.

As automarkup.py should be able to handle those cases, let's
just get rid of the markup.

While not required by automarkup, in order to make easier for
grep, both type and names are now at the same line.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>