package/prserv: Merge two similar functions into one

Having these two separate functions handling PR values seems pointless,
and worse, there are impossible code branches mixed within them.

Merge them into one function and tweak comments so at least you
don't have to read both functions to figure out what is going on.

This does restructure the conditionals to try and aid readability.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>