power: smb5-lib: fix DPDM regulator handling

There is a possibility of unbalanced request for DPDM
regulator due to race between handling of plugin and
detach_detection_work(PR_SWAP handling), fix this by
adding proper locking and caching regulator state.

Change-Id: I67ff3233a6dabce45d889003b4261de970ad37cf
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>