media: ext-ctrls-codec.rst: simplify a few tables

Those tables nicely fits on PDF output without any hack.
Yet, they are using a very small font, and have tabularcolumns.

Clean it up, and convert it to an ASCII artwork, as it
makes easier to see that no hacks are needed to display it ;-)

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