On x86 platforms the EC provides a way to read 'switches', which are
on/off values determined by the EC.
Add a new driver method for this and implement it for LPC.
Signed-off-by: Simon Glass <sjg@chromium.org>
This is used several times in this file. Put it in a function to avoid
code duplication.
Also add a test for this function. There are no cros_ec tests at present,
so it is time to update the code.
Signed-off-by: Simon Glass <sjg@chromium.org>