sunxi: icnova-a20-swac_defconfig: Remove AXP209_POWER

Remove the AXP209_POWER option from SYS_EXTRA_OPTIONS.
As this configuration already exists on Kconfig, we just need
to remove it from defconfig.

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>