rust: pl011: use default set of lints

rust: pl011: use default set of lints

Being the first crate added to QEMU, pl011 has a rather restrictive
Clippy setup.  This can be sometimes a bit too heavy on its suggestions,
for example

error: this could be a `const fn`
   --> hw/char/pl011/src/device.rs:382:5
    |
382 | /     fn set_read_trigger(&mut self) {
383 | |         self.read_trigger = 1;
384 | |     }
    | |_____^

Just use the standard set that is present in rust/Cargo.toml, with
just a small adjustment to allow upper case acronyms which are used
for register names.

Reported-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>