dt-bindings: perf: starfive: Add JH8100 StarLink PMU

Add device tree binding for StarFive's JH8100 StarLink PMU (Performance
Monitor Unit).

Signed-off-by: Ji Sheng Teoh <jisheng.teoh@starfivetech.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240229072720.3987876-3-jisheng.teoh@starfivetech.com
Signed-off-by: Will Deacon <will@kernel.org>