ARM: sunxi: Really enable LRADC keys in sunxi_defconfig

Commit be8becb8 ("ARM: sunxi_defconfig: Enable LRADC keys
(KEYBOARD_SUN4I_LRADC)") added CONFIG_KEYBOARD_SUN4I_LRADC=y to
sunxi_defconfig. However, it depends on CONFIG_KEYBOARD which is
explicitly disabled in sunxi_defconfig. Hence, the LRADC keys were
never actually enabled. Remove the line disabling CONFIG_KEYBOARD in
order to really enable KEYBOARD_SUN4I_LRADC.

Signed-off-by: Timo Sigurdsson <public_timo.s@silentcreek.de>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>