sandbox: capsule: Enable EFI capsule module on sandbox variants

Enable the EFI capsule update code on all sandbox variants. This was
already enabled on the sandbox, sandbox64 and sandbox_flattree
variants. The rest of the variants also have the EFI capsule update
module  enabled now. With this commit, the mkeficapsule tool also gets
enabled on all variants.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>