ARM: dts: socfpga: remove the reg property in the pmu

ARM: dts: socfpga: remove the reg property in the pmu

The Cortex-A9 PMU accesses the hardware via system coprocessor registers,
not memory-mapped I/O. The driver does not parse or use a 'reg' property
from the device tree, so we can remove the reg from the DTS.

This change fixes this dtbs_check warning:

(arm,cortex-a9-pmu): 'reg' does not match any of the regexes

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>