boot: Unify protocol opening

boot: Unify protocol opening

We are using HandleProtocol everywhere except in these few cases. This
unifies on HandleProtocol as it is simpler to use and equivalent to
OpenProtocol.

The only difference between the two is that OpenProtocol attributes the
opened protocol to a firmware-owned handle instead of our image handle.
This has no real use for regular UEFI applications as any protocols
opened via BY_HANDLE or GET_PROTOCOL is not required to be closed. In
fact, when a protocol is uninstalled it will do nothing more than reduce
the open count for these.