NTB: debugfs device entry

Create a debugfs entry for the NTB device to log the basic device info,
as well as display the error count on a number of registers.

Signed-off-by: Jon Mason <jon.mason@intel.com>

diff --cc drivers/ntb/ntb_hw.c
Simple merge

diff --cc drivers/ntb/ntb_hw.h
Simple merge

diff --cc drivers/ntb/ntb_regs.h
Simple merge