ARM: dts: sun8i: replace enable-sdio-wakeup with wakeup-source for BananaPi M1+

Though the mmc core driver will continue to support the legacy
"enable-sdio-wakeup" property to enable SDIO as the wakeup source,
"wakeup-source" is the new standard binding.

This patch replaces the legacy "enable-sdio-wakeup" with the unified
"wakeup-source" property in order to avoid any further copy-paste
duplication.

Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>