configs: meson64_android: implement A/B slot support

configs: meson64_android: implement A/B slot support

Implement A/B slot selection using the U-Boot ab_select command.

Keep support for non A/B.

Not: We need to redefine the recovery partition label, as RecoveryOS
is included in the boot image for A/B systems [1]

[1] https://source.android.com/devices/tech/ota/ab/ab_implement#recovery
Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>