NTB: Rename Variables for NTB-RP

Many variable names in the NTB driver refer to the primary or secondary
side.  However, these variables will be used to access the reverse case
when in NTB-RP mode.  Make these names more generic in anticipation of
NTB-RP support.

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_transport.c
Simple merge