ARM: dts: imx53-ppd: Enable secure-reg-access

Add 'secure-reg-access' property to enable PMU and hardware counters
so that they can be properly used with the 'perf' tool.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
[fabio: kept the change only in imx53-ppd context]
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>