wil6210: add documentation for 11ad vdd LDO supply and new SMMU API

On some platforms there is a LDO that powers the 11ad card.
New SMMU API configuration added.
Add documentation for that LDO and SMMU API.

Change-Id: I6e495038133aedc7a65ff4f582a7206e7f0bd488
Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>