Simplify error handling by converting the driver to use managed
allocations and initializations.

Note that platform_get_resource() and ioremap_nocache() are combined in
devm_platform_ioremap_resource().
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>