Support checking for specific device-getter api support

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

include/rocm_smi/rocm_smi_device.h

@@ -194,6 +194,8 @@ class Device {
     SupportedFuncMap *supported_funcs(void) {return &supported_funcs_;}
     void fillSupportedFuncs(void);
     void DumpSupportedFunctions(void);
+    bool DeviceAPISupported(std::string name, uint64_t variant,
+                                                        uint64_t sub_variant);
 
  private:
     std::shared_ptr<Monitor> monitor_;