doc-rst: userp: Add ioctl cross references

There are lots of ioctls mentioned there that aren't cross-referenced.

Convert the const to cross references. That makes it visually
better, and improves navigation along the document.

While here, remove bad whitespaces.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
1 file changed