docs: pti_intel_mid.txt: convert it to pti_intel_mid.rst

Convert this small file to ReST format and rename it.

Most of the conversion were related to adjusting whitespaces
in order for each section to be properly parsed.

While this is not part of any book, mark it as :orphan:, in order
to avoid build warnings.

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