Add a hex dump utility for use in KDL commands
VFS FIFO: Fix RingBuffer::Read()/Write() return types

size_t -> ssize_t, since they may actually return an error code.
VFS FIFO: Enlarge FIFO buffer sizes

* Increase FIFO buffer capacity from 32 to 64 KiB and the FIFO atomic
  write size ({BUF_SIZE}) from 512 bytes to 4 KiB (both like Linux).
* Fix *pathconf(..., _PC_PIPE_BUF). It was returning 4 KiB although the
  implemented atomic write size was 512 bytes only. Now both *pathconf()
  and the FIFO implementation refer to the same constant.
VFS FIFO: Add "fifo" KDL command

Prints information about a FIFO node and, optionally, its data buffer
content.