NTB: add helper functions to set and clear sideinfo

We define two new helper functions to set and clear
sideinfo registers respectively. These functions
take an additional boolean parameter which signifies
whether we want to set/clear the sideinfo register
of the peer(true) or local host(false).

Signed-off-by: Arindam Nath <arindam.nath@amd.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>