power: smb5-lib: Register typec partner only when partner is unregistered

Fix an issue where the type-C partner tries to register
without a unregister.

While at it, PMI632 does not support TRY.SNK, do not enable it.

Change-Id: I452f73d0841d160b76645981227a077564e167e1
Signed-off-by: Kavya Nunna <knunna@codeaurora.org>