ARM: mach-shmobile: sh73a0: Minimal setup using DT

Allow a minimal setup of the sh73a0 SoC using a flattened device tree.
In particular, Configure the i2c controllers using a flattened device tree.

SCI serial controller and CMT clock source, whose drivers do not yet
support configuration using a flattened device tree, are still configured
using C code in order to allow booting of a board with this SoC.

*** Please note that the clock initialisation scheme used in
    this patch does not currently work with SMP as there
    is a yet to be resolved lock-up in workqueue initialisation.

    CONFIG_SMP must be disabled when using this code. ***

Includes update from Thierry Reding to no longer use gic_handle_irq()

Cc: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
fix