arm64: dts: berlin4ct: switch to Cortex-A53 specific pmu nodes

Commit ac82d127 ("arm64: perf: add Cortex-A53 support") adds the
cortex A53 PMU support, thus instead of using the generic armv8-pmuv3
compatibility use the more specific Cortex A53 compatibility.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>