Add an unlink method to block driver interface.  Same motivataion as for the same modification to the character driver interface

Pipes/FIFOs:  Implement the unlink method.  If the pipe/FIFO is unlinked, it will marked the pipe/FIFO as unliked.  If/when all open references to the driver are closed, all of the driver resources will be freed.

VFS:  Add an unlink method to the character driver interface.  This is important because if the character driver inode is unlinked and there are no open references to the driver, then the driver resources will be stranded.  On the unlink call, the driver has the opportunity (1) check if there an any open references, and (2) if not free the driver resources

If a Unix domain socket is non-blocking, then the underlying FIFO should also be opened non-blocking

Unix domain/FIFOs:  Fix a race condition between FIFO buffer operations and the opening and closing of FIFOs which necessary when the FIFOs are used to support Unix domain, datagram sockets.  The default policy is the deallocate FIFO buffering when the last client closes the pipe.  When when used for datagram communicatinos, packets left in the FIFO will be lost.  Some like UDP read-ahead is needed:  The buffered data in the FIFO needs to be retained until the reader gets a chance to re-open the FIFO.  Added an ioctl (PIPEIOC_POLICY) to control the buffer policy. Default (0) is the legacy behavior; Unix domain datagram logic sets the alternative policy so that the packet data persists after the FIFO is closed.

EFM32: Logic to unconditionally enable LE clocking. Even you don't use core clock LE as source for LFA or LFB, to read are write any register not clocked by HFPERCLK or HFCORECLK, HFCORECLKLE should be enabled.  From Pierre-noel Bouteville.

Networking:  Separate TCP poll logic out of net/sockets/net_poll.c and move it into the new net/tcp/tcp_netpoll.c.

Networking:  Separate out UDP poll logic from socket/net_poll.c into a new udp/udp_netpoll.c; Create a skeleton local/local_netpoll.c for future poll support on Unix domain sockets.