Split the get/set device_attr helpers instead of using a boolean param to
select between get and set.  Duplicating upper level wrappers is a very,
very small price to pay for improved readability, and having constant (at
compile time) inputs will allow the selftests framework to sanity check
ioctl() invocations.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>