cmd: update smbios cmd

cmd: update smbios cmd

Update the cmd according to the changes of the smbios library:
1. Refactor smbios cmd print functions to match the content defined
   by the specification.
2. Add new print functions for Type 3, 4 and 7.
3. Remove the fallback string "Not specified" from smbios_get_string,
   as the spec requires a NULL output for those undefined strings.
4. Update the test_cmd_smbios_sandbox pytest expected result to
   align with the smbios library changes and add new pytest
   test_cmd_smbios_sysinfo_verbose to test the verbose smbios
   output.

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>