smbios: Fix SMBIOS tables

Commit e4f8e543("smbios: Drop the unused Kconfig options")
break SMBIOS tables.  The reason is that the patch drops the Kconfig
options *after* removing the code using them,  but that changes the semantics
of the code completely.  Prior to the change a non NULL value was used in
the 'product' and 'manufacturer ' fields.

Chapter 6.2 of the DMTF spec requires Manufacturer and Product Name to be
non-null on some of the tables. So let's add sane defaults for Type1/2/3.

* Before the patchset:

<snip>
Handle 0x0002, DMI type 2, 14 bytes
Base Board Information
        Manufacturer: Not Specified
        Product Name: Not Specified
        Version: Not Specified
        Serial Number: Not Specified
        Asset Tag: Not Specified
        Features:
                Board is a hosting board
        Location In Chassis: Not Specified
        Chassis Handle: 0x0000
        Type: Motherboard

Invalid entry length (0). DMI table is broken! Stop.

* After the patchset:

<snip>
Handle 0x0005, DMI type 32, 11 bytes
System Boot Information
        Status: No errors detected

Handle 0x0006, DMI type 127, 4 bytes
End Of Table

Fixes: e4f8e543 ("smbios: Drop the unused Kconfig options")
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>