sysinfo: Require that sysinfo_detect be called before other methods

This has the uclass enforce calling detect() before other methods.  This
allows drivers to cache information in detect() and perform (cheaper)
retrieval in the other accessors. This also modifies the only instance
where this sequencing was not followed.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>