Kernel/USB: Add UKBuffer variants of certain BulkPipe/Transfer functions

These will be useful for directly accessing the source/destination
buffers, without going through a third buffer first.

Kernel/Bus/USB/USBTransfer.h

@@ -30,6 +30,7 @@ public:
     void set_error_occurred() { m_error_occurred = true; }
 
     ErrorOr<void> write_buffer(u16 len, void* data);
+    ErrorOr<void> write_buffer(u16 len, UserOrKernelBuffer data);
 
     // `const` here makes sure we don't blow up by writing to a physical address
     USBRequestData const& request() const { return m_request; }