smbios: Require the caller to align the SMBIOS table

All callers handle this alignment, so drop the unnecessary code. This
simplifies things a little.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>