docs: def get_supported_boot_mode(self):
          """Retrieves the supported boot mode.
  
          :returns: any one of the following proliantutils.ilo.constants:
  
              SUPPORTED_BOOT_MODE_LEGACY_BIOS_ONLY,
              SUPPORTED_BOOT_MODE_UEFI_ONLY,
              SUPPORTED_BOOT_MODE_LEGACY_BIOS_AND_UEFI
  
          """
          system = self._get_host_details()
          bios_uefi_class_val = 0  # value for bios_only boot mode
          if ('Bios' in system['Oem']['Hp'] and
                  'UefiClass' in system['Oem']['Hp']['Bios']):
              bios_uefi_class_val = (system['Oem']['Hp']
                                           ['Bios']['UefiClass'])
          return mappings.GET_SUPPORTED_BOOT_MODE_RIS_MAP.get(
              bios_uefi_class_val)