For A/B system update support the Android boot process requires to send
'androidboot.slot_suffix' parameter as a command line argument. This
patch implementes 'ab_select' command which allows us to obtain current
slot by processing the A/B metadata.
The patch was extracted from commit [1] with one modification: the
separator for specifying the name of metadata partition was changed
from ';' to '#', because ';' is used for commands separation.
Signed-off-by: Ruslan Trofymenko <ruslan.trofymenko@linaro.org> Signed-off-by: Igor Opaniuk <igor.opaniuk@gmail.com> Reviewed-by: Alistair Strachan <astrachan@google.com> Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org> Reviewed-by: Simon Glass <sjg@chromium.org>