power: smb5: Enable read/writing of Type-C Rp value

Enable the reading and writing of the Rp value used exclusively in
Type-C Source mode operation.

CRs-Fixed: 2283665
Change-Id: I806c0459e59d41cd9a24055cf4c160adbd88b594
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>