MAINTAINERS: Remove myself from HiSilicon PMU maintainers

Remove myself as I'm leaving HiSilicon and not suitable for maintaining
this. Thanks for the journey.

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Acked-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Will Deacon <will@kernel.org>