arm64: dts: hikey960: Define wl1837 power capabilities

These properties are required for compatibility with runtime PM.
Without these properties, MMC host controller will not be aware
of power capabilities. When the wlcore driver attempts to power
on the device, it will erroneously fail with -EACCES. This fixes
a regression found here: https://lkml.org/lkml/2018/6/12/930



Fixes: 60f36637 ("wlcore: sdio: allow pm to handle sdio power")
Signed-off-by: Ryan Grachek <ryan@edited.us>
Tested-by: John Stultz <john.stultz@linaro.org>
Acked-by: John Stultz <john.stultz@linaro.org>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>