smbios: Fix warning when building with clang

smbios: Fix warning when building with clang

When building with clang, we see warnings such as:
error: field max_size within 'struct smbios_type7' is less aligned than
'union cache_size_word' and is usually due to 'struct smbios_type7'
being packed, which can lead to unaligned accesses
[-Werror,-Wunaligned-access]
when building drivers/sysinfo/smbios.c. Resolve this error by packing
the unions as well after verifying they are complete (16 or 32 bits).

Reviewed-by: Raymond Mao <raymondmaoca@gmail.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Tom Rini <trini@konsulko.com>