[libc] Treat the locks array as a bitfield

Currently we keep an internal buffer of device memory that is used to
indicate ownership of a port. Since we only use this as a single bit we
can simply turn this into a bitfield. I did this manually rather than
having a separate type as we need very special handling of the masks
used to interact with the locks.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D155511

libc/utils/gpu/server/rpc_server.cpp

@@ -23,7 +23,7 @@ using namespace __llvm_libc;
 static_assert(sizeof(rpc_buffer_t) == sizeof(rpc::Buffer),
               "Buffer size mismatch");
 
-static_assert(RPC_MAXIMUM_PORT_COUNT == rpc::DEFAULT_PORT_COUNT,
+static_assert(RPC_MAXIMUM_PORT_COUNT == rpc::MAX_PORT_COUNT,
               "Incorrect maximum port count");
 
 // The client needs to support different lane sizes for the SIMT model. Because