MAINTAINERS: Add entry for StarFive StarLink PMU

Add maintainer entry for StarFive StarLink PMU driver, and mark it as
"Maintained"

Signed-off-by: Ji Sheng Teoh <jisheng.teoh@starfivetech.com>
Link: https://lore.kernel.org/r/20240229072720.3987876-5-jisheng.teoh@starfivetech.com


Signed-off-by: Will Deacon <will@kernel.org>