ARM: rcar-gen2: Do not setup timer in non-secure mode

If the system has been started in non-secure mode, then the ARM generic
timer is not configurable during the kernel initialisation. Currently
the only thing we can check for is if the timer has been correctly
configured during the boot process.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Ian Molton <ian.molton@codethink.co.uk>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>