For device-getter functions, allow users to specify a nullptr
for the provided buffer. In those cases, the function will return
RSMI_STATUS_NOT_SUPPORTED if the hardware or system software does
not support the function. If the function is supported, then
RSMI_STATUS_INVALID_ARGS will be returned, unless a different
error is encountered.
Additionally, tests and documentation were updated to reflect
this change.
Change-Id: Ie7db3a4c8c66af97ebd7ee1e3b95cd331ace9d9c
Chris Freehill